Golf balls having dual-layered cores with metal-containing centers and dual-layered covers

ABSTRACT

Multi-piece golf balls containing a dual-layered core and dual-layered cover are provided. The core structure includes a small, heavy inner core (center) having a relatively high specific gravity, and a surrounding outer core layer. The core layers may have different hardness gradients. The center of the core comprises a metal material such as copper, steel, brass, tungsten, titanium, aluminum, and combinations and alloys thereof preferably dispersed in a thermoplastic polymeric matrix. The outer core layer is preferably formed from a thermoset composition such as polybutadiene. The multi-layered cores and covers have selective specific gravity relationships between the different layers. This helps provide the ball with good flight distance and spin control. The resulting balls have good resiliency and other playing performance properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending, co-assigned U.S.patent application Ser. No. 15/628,716 filed Jun. 21, 2017, now allowed,which is a continuation-in-part of co-assigned U.S. patent applicationSer. No. 15/387,911 filed Dec. 22, 2016, now issued as U.S. Pat. No.10,080,926 with an issue date of Sep. 25, 2018, which is acontinuation-in-part of co-assigned U.S. patent application Ser. No.14/711,962, filed May 14, 2015, now issued as U.S. Pat. No. 9,878,213with an issue date of Jan. 30, 2018, which is a continuation-in-part ofco-assigned U.S. patent application Ser. No. 13/606,099, filed Sep. 7,2012, now issued as U.S. Pat. No. 9,095,746 with an issue date of Aug.4, 2015, the entire disclosures of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention generally relates to multi-piece golf balls havinga solid core of at least two layers and cover of at least one layer. Inone embodiment, the ball contains a dual-layered core having a small,heavy inner core (center) and surrounding outer core layer. The centercomprises a metal material and the outer core layer preferably comprisesa thermoset material such as polybutadiene rubber. In anotherembodiment, the ball contains a multi-layered core having a small, heavyinner core (center), intermediate core layer, and surrounding outer corelayer. The core layers have different hardness gradients and specificgravity values to provide finished balls having high resiliency andspin-control properties.

Brief Review of the Related Art

Multi-piece, solid golf balls having a solid inner core protected by acover are used today by recreational and professional golfers. The golfballs may have single-layered or multi-layered cores. Normally, the corelayers are made of a highly resilient natural or synthetic rubbermaterial such as styrene butadiene, polybutadiene, poly(cis-isoprene),or poly(trans-isoprene); or highly neutralized ethylene acid copolymers(HNPs). The covers may be single or multi-layered and made of a durablematerial such as HNPs, polyamides, polyesters, polyurethanes, orpolyureas. Manufacturers of golf balls use different constructions (forexample, three-piece, four-piece, and five-piece balls) to impartspecific properties and features to the balls.

The core is the primary source of resiliency for the golf ball and isoften referred to as the “engine” of the ball. The resiliency orcoefficient of restitution (“COR”) of a golf ball (or golf ballcomponent, particularly a core) means the ratio of a ball's reboundvelocity to its initial incoming velocity when the ball is fired out ofan air cannon into a rigid plate. The COR for a golf ball is written asa decimal value between zero and one. A golf ball may have different CORvalues at different initial velocities. The United States GolfAssociation (USGA) sets limits on the initial velocity of the ball soone objective of golf ball manufacturers is to maximize the COR underthese conditions. Balls (or cores) with a high rebound velocity have arelatively high COR value. Such golf balls rebound faster, retain moretotal energy when struck with a club, and have longer flight distancesas opposed to balls with lower COR values. Ball resiliency and CORproperties are particularly important for long distance shots. Forexample, balls having high resiliency and COR values tend to travel afar distance when struck by a driver club from a tee. The spin rate ofthe ball also is an important property. Balls having a relatively highspin rate are particularly desirable for relatively short distance shotsmade with irons and wedge clubs. Professional and highly skilledrecreational golfers can place a back-spin on such balls more easily. Byplacing the right amount of spin and touch on the ball, the golfer hasbetter control over shot accuracy and placement. This is particularlyimportant for approach shots near the green and helps improve scoringperformance.

Over the years, golf ball manufacturers have looked at adjusting thedensity or specific gravity among the multiple layers of the golf ballto control its spin rate. In general, the total weight of a golf ballhas to conform to weight limits set by the United States GolfAssociation (“USGA”). Although the total weight of the golf ball ismandated, the distribution of weight within the ball can vary.Redistributing the weight or mass of the golf ball either towards thecenter of the ball or towards the outer surface of the ball changes itsflight and spin properties.

For example, the weight can be shifted towards the center of the ball toincrease the spin rate of the ball as described in Yamada, U.S. Pat. No.4,625,964. In the '964 Patent, the core composition preferably contains100 parts by weight of polybutadiene rubber; 10 to 50 parts by weight ofzinc acrylate or zinc methacrylate; 10 to 150 parts by weight of zincoxide; and 1 to 5 parts by weight of peroxide as a cross-linking orcuring agent. The inner core has a specific gravity of at least 1.50 inorder to make the spin rate of the ball comparable to wound balls. Theball further includes a cover an intermediate layer disposed between thecore and cover, wherein the intermediate layer has a lower specificgravity than the core.

Chikaraishi et al., U.S. Pat. No. 5,048,838 discloses a three-piece golfball containing a two-piece solid core and a cover. The inner core has adiameter in the range of 15-25 mm, a weight of 2-14 grams, a specificgravity of 1.2 to 4.0, and a hardness of 55-80 JISC. The specificgravity of the outer core layer is less than the specific gravity of theinner core by 0.1 to 3.0. less than the specific gravity of the innercore. The inner and outer core layers are formed from rubbercompositions.

Gentiluomo, U.S. Pat. No. 5,104,126 discloses a three-piece ball with adense inner core made of steel, lead, brass, zinc, copper, and a filledelastomer, wherein the core has a specific gravity of at least 1.25. Theinner core is encapsulated by a lower density syntactic foamcomposition, and the core construction is encapsulated by an ionomercover.

Yabuki et al., U.S. Pat. No. 5,482,285 discloses a three-piece golf ballhaving an inner core and outer core encapsulated by an ionomer cover.The specific gravity of the outer core is reduced so that it fallswithin the range of 0.2 to 1.0. The specific gravity of the inner coreis adjusted so that the total weight of the inner/outer core fallswithin a range of 32.0 to 39.0 g.

Nesbitt and Binette, U.S. Pat. No. 6,277,934 disclose a non-wound,multi-piece golf ball containing a spherical metal core component havinga specific gravity of about 1.5 to about 19.4; and an outer core layerdisposed about said spherical metal core component, wherein the corelayer has a specific gravity of less than 1.2. The metal core ispreferably contains a metal selected from steel, titanium, brass, lead,tungsten, molybdenum, copper, nickel, iron, and combinations thereof.Polybutadiene rubber compositions containing metallic powders can beused to form the core. The core assembly preferably has a coefficient ofrestitution of at least 0.730.

Sullivan, U.S. Pat. No. 6,494,795 discloses a golf ball comprising aninner core having a specific gravity of greater than 1.8 encased withina first mantle surrounding the inner core. A portion of the first mantlecomprises a low specific gravity layer having a specific gravity of lessthan 0.9. The core may be made from a high density metal or from metalpowder encased in a polymeric binder. High density metals such as steel,tungsten, lead, brass, bronze, copper, nickel, molybdenum, or alloys maybe used. The mantle layer surrounding the inner core may be made from athermoset or thermoplastic material such as epoxy, urethane, polyester,polyurethane, or polyurea.

Sullivan, U.S. Pat. No. 6,692,380 discloses a golf ball comprising aninner core having a specific gravity of at least 3, a diameter of about0.40 to about 0.60 inches and preferably comprises a polymeric matrix ofpolyurethane, polyurea, or blends thereof. The outer core may be madefrom a polybutadiene rubber. The specific gravity of the compositionsmay be adjusted by adding fillers such as metal powder, metal alloypowder, metal oxide, metal stearates, particulates, and carbonaceousmaterial.

Morgan and Jones, U.S. Pat. No. 6,986,717 discloses a golf ballcontaining a high-specific gravity central sphere encapsulated in a softand resilient shell, preferably formed of a polybutadiene rubber. Thisshell is subsequently wound with thread that is preferably elastic toform a wound core. This wound core is then covered with a cover materialsuch as balata, gutta percha, an ionomer or a blend of ionomers,polyurethane, polyurea-based composition, and epoxy-urethane-basedcompositions. The sphere is formed of metallic powder and a thermoset orthermoplastic binder material. Metals such as tungsten, steel, brass,titanium, lead, zinc, copper, bismuth, nickel, molybdenum, iron, bronze,cobalt, silver, platinum, and gold can be used. Preferably, the metalsphere has a specific gravity of at least 6.0 and a diameter of lessthan 0.5 inches.

Although some conventional multi-layered core constructions aregenerally effective in providing high resiliency golf balls, there is acontinuing need for improved core constructions in golf balls.Particularly, it would be desirable to have multi-layered coreconstructions with selective specific gravities and mass densities toprovide the ball with good flight distance along with spin control. Thepresent invention provides core constructions and golf balls having suchproperties as well as other advantageous features, and benefits.

SUMMARY OF THE INVENTION

The present invention generally relates to multi-layered golf balls andmore particularly to golf balls having a dual core. The ball preferablycomprises a dual core having an inner core and surrounding outer corelayer; and a cover having at least one layer disposed about the corestructure. The inner core preferably has a diameter in the range ofabout 0.100 to about 1.100 inches; a specific gravity (SG_(inner core));and an outer surface hardness (H_(center surface)) and a center hardness(H_(center)), the H_(center surface) being greater than the H_(center)to provide a positive hardness gradient. The surrounding outer corelayer comprises a thermoset or thermoplastic composition and preferablyhas a thickness in the range of about 0.200 to about 1.200 inches; aspecific gravity (SG_(outer core)); and an outer surface hardness(H_(outer surface of OC)) and a midpoint hardness (H_(midpoint)), theH_(outer surface of OC) being greater than the (H_(midpoint)) to providea positive hardness gradient.

The core layers may have different hardness gradients. For example, theinner core may have a positive hardness gradient; and the outer corelayer may have a zero or negative hardness gradient. In anotherembodiment, the inner core may have a zero or negative hardnessgradient; and the outer core layer may have a positive hardnessgradient. Still yet, in another version, both the inner core and outercore layers have zero or negative hardness gradients.

In one preferred embodiment, a four-piece ball, having two cover layersdisposed about the multi-layered core, is made. The cover layer has aspecific gravity (SG_(cover)). Preferably, the SG_(inner core) isgreater than the SG_(outer core) and the SG_(outer core) issubstantially equal to the SG_(cover). In another embodiment, afour-piece ball, having a dual-layered cover layer disposed about thedual-layered core, is made. The inner cover layer has a specific gravity(SG_(inner cover)); and the outer cover layer has a specific gravity(SG_(outer cover)). In one preferred embodiment, the SG_(inner core) isgreater than the SG_(outer core) and the SG_(outer core) issubstantially equal to the SG_(inner cover) and SG_(outer cover).Preferably, the inner core has a specific gravity in the range of about1.50 to about 16.25. In one embodiment, the specific gravity is in therange of about 1.90 to about 9.70; and in another embodiment, thespecific gravity is in the range of about 6.00 to about 13.80.

Various metals may be used in the compositions of this invention. In oneparticularly preferred version, the thermoplastic composition comprisesa metal selected from the group consisting of copper, steel, brass,tungsten, titanium, aluminum, magnesium, molybdenum, cobalt, nickel,iron, tin, bronze, silver, gold, platinum, zinc, lithium, manganese,scandium, sodium, calcium, zirconium, vanadium, niobium, silicon,selenium, boron, chromium, and alloys and combinations and alloys andcombinations thereof. These multi-layered core constructions withmetal-containing centers have selective specific gravity relationshipsbetween the different layers. This helps provide the ball with goodflight distance and spin control. The resulting balls have goodresiliency and other playing performance properties.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are characteristic of the present invention areset forth in the appended claims. However, the preferred embodiments ofthe invention, together with further objects and attendant advantages,are best understood by reference to the following detailed descriptionin connection with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a three-piece golf ball having adual-layered core made in accordance with the present invention;

FIG. 2 is a cross-sectional view of a four-piece golf ball having adual-layered core made in accordance with the present invention;

FIG. 3 is a cross-sectional view of a two-piece golf ball having asingle-layered core and single-layered cover made in accordance with thepresent invention; and

FIG. 4 is a cross-sectional view of a five-piece golf ball having adual-layered core, an intermediate layer, and a dual-layered cover madein accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Golf Ball Constructions

Golf balls having various constructions may be made in accordance withthis invention. For example, golf balls having three-piece, four-piece,and five-piece constructions with single or multi-layered covermaterials may be made. The term, “layer” as used herein means generallyany spherical portion of the golf ball. More particularly, in oneversion, a three-piece golf ball having a dual-core and cover is made.The dual-core includes an inner core (center) and surrounding outer corelayer. In another version, a four-piece golf ball comprising a dual-coreand dual-cover (inner cover and outer cover layers) is made. In yetanother construction, a four-piece or five-piece golf ball having amulti-layered core; an intermediate (casing) layer, and cover layer(s)may be made. As used herein, the term, “intermediate layer” means alayer of the ball disposed between the core and cover. The intermediatelayer also may be referred to as a casing or mantle layer. The diameterand thickness of the different layers along with properties such ashardness and compression may vary depending upon the construction anddesired playing performance properties of the golf ball.

Referring to FIG. 1, one version of a golf ball that can be made inaccordance with this invention is generally indicated at (12). The ball(12) contains a multi-layered core (14) having an inner core (center)(14 a) and outer core layer (14 b) surrounded by a single-layered cover(16). The inner core (14 a) is relatively small in volume and generallyhas a diameter within a range of about 0.10 to about 1.10 inches. Moreparticularly, the inner core (14 a) preferably has a diameter size witha lower limit of about 0.15 or 0.25 or 0.35 or 0.45 or 0.55 inches andan upper limit of about 0.60 or 0.70 or 0.80 or 0.90 inches. In onepreferred version, the diameter of the inner core (14 a) is in the rangeof about 0.025 to about 0.080 inches, more preferably about 0.030 toabout 0.075 inches. Meanwhile, the outer core layer (14 b) generally hasa thickness within a range of about 0.010 to about 0.250 inches andpreferably has a lower limit of 0.010 or 0.020 or 0.025 or 0.030 inchesand an upper limit of 0.070 or 0.080 or 0.100 or 0.200 inches. In onepreferred version, the outer core layer has a thickness in the range ofabout 0.040 to about 0.170 inches, more preferably about 0.060 to about0.150 inches. Referring to FIG. 2, in another version, the golf ball(18) contains a dual-core (20) having an inner core (center) (20 a) andouter core layer (20 b). The dual-core (20) is surrounded by amulti-layered cover (22) having an inner cover layer (22 a) and outercover layer (22 b).

Golf balls made in accordance with this invention can be of any size,although the USGA requires that golf balls used in competition have adiameter of at least 1.68 inches. For play outside of United States GolfAssociation (USGA) rules, the golf balls can be of a smaller size.Normally, golf balls are manufactured in accordance with USGArequirements and have a diameter in the range of about 1.68 to about1.80 inches. In general, the multi-layer core structure (14) has anoverall diameter within a range having a lower limit of about 1.00 or1.20 or 1.30 or 1.40 inches and an upper limit of about 1.58 or 1.60 or1.62 or 1.66 inches, and more preferably in the range of about 1.3 to1.65 inches. In one embodiment, the diameter of the core subassembly(14) is in the range of about 1.45 to about 1.62 inches.

As discussed further below, various compositions may be used to make thedual-core structures of the golf balls of this invention. The golf ballsmay contain certain fillers to adjust the specific gravity and weight ofthe core layers as needed. In general, the inner core (center) has aspecific gravity within a range having a lower limit of about 1.18 or1.50 or 2.00 or 2.50 g/cc and an upper limit of about 3.00 or 3.50 or4.00 or 4.50 or 5.00 g/cc. In a preferred embodiment, the inner core hasa specific gravity of about 1.20 to about 3.50 g/cc, more preferablyabout 1.25 to about 3.00 g/cc. Meanwhile, the outer core layer (14 b)preferably has a relatively low specific gravity. The outer core layer(14 b) generally has a specific gravity within a range having a lowerlimit of about 0.080 or 0.100 or 0.400 or 0.600 or 0.800 g/cc and anupper limit of about 1.00 or 1.10 or 1.20 g/cc. The amount of fillersused in the compositions is adjusted so the weight of the golf ball doesnot exceed limits set by USGA rules. The USGA has established a maximumweight of 45.93 g (1.62 ounces). For play outside of USGA rules, thegolf balls can be heavier. In one preferred embodiment, the weight ofthe multi-layered core is in the range of about 28 to about 38 grams.

Inner Core Composition

Preferably, the inner core composition comprises a metal material suchas, for example, copper, steel, brass, tungsten, titanium, aluminum,magnesium, molybdenum, cobalt, nickel, iron, lead, tin, bronze, silver,gold, and platinum, and alloys and combinations thereof. The metalmaterial may be dispersed in a polymeric matrix comprising a thermosetrubber or thermoplastic material and plasticizer. The metal material isdispersed uniformly in the polymeric matrix to provide a substantiallyhomogenous composition. The metal material is blended fully into thepolymeric matrix to prevent agglomerates and aggregates from beingformed. The resulting metal-containing composition is used to form aninner core structure having a relatively high specific gravity, therebyproviding a ball having a lower moment of inertia as discussed furtherbelow.

In one version, a thermoplastic material is used as the polymeric binder(matrix) in the composition for making the inner core. Suitablethermoplastic materials that can be used to make the inner and outercore layers are described further below. These thermoplastic polymersinclude, for example, ethylene acid copolymers containing acid groupsthat are at least partially neutralized. Preferably, the neutralizationlevel is greater than 70%, more preferably at least 90%, and even morepreferably at least 100%. Such ethylene acid copolymers having aneutralization level of 70% or greater are commonly referred to ashighly neutralized polymers (HNPs).

Suitable ethylene acid copolymers that may be used to form thethermoplastic compositions of this invention are generally referred toas copolymers of ethylene; C₃ to C₈ α, β-ethylenically unsaturatedmono-or dicarboxylic acid; and optional softening monomer. Copolymersmay include, without limitation, ethylene acid copolymers, such asethylene/(meth)acrylic acid, ethylene/(meth)acrylic acid/maleicanhydride, ethylene/(meth)acrylic acid/maleic acid mono-ester,ethylene/maleic acid, ethylene/maleic acid mono-ester,ethylene/(meth)acrylic acid/n-butyl (meth)acrylate,ethylene/(meth)acrylic acid/iso-butyl (meth)acrylate,ethylene/(meth)acrylic acid/methyl (meth)acrylate,ethylene/(meth)acrylic acid/ethyl (meth)acrylate terpolymers, and thelike. Other thermoplastics such as polyamides, polyamide-ethers, andpolyamide-esters, polyurethanes, polyureas, polyurethane-polyureahybrids, polyesters, polyolefins, polystyrenes, and blends thereof maybe used.

In another version, a thermoset rubber material is used as the polymericbinder (matrix) in the composition for making the inner core. In thepresent invention, thermoset rubber materials also are preferably usedfor making the outer core layer. Suitable thermoset rubber materialsthat can be used to make the inner and outer core layers in accordancewith this invention are described further below. Suitable thermosetrubber materials that may be used as the polymeric binder (matrix)material are natural and synthetic rubbers including, but not limitedto, polybutadiene, polyisoprene, ethylene propylene rubber (“EPR”),ethylene-propylene-diene (“EPDM”) rubber, styrene-butadiene rubber,styrenic block copolymer rubbers (such as “SI”, “SIS”, “SB”, “SBS”,“SIBS”, and the like, where “S” is styrene, “I” is isobutylene, and “B”is butadiene), polyalkenamers such as, for example, polyoctenamer, butylrubber, halobutyl rubber, polystyrene elastomers, polyethyleneelastomers, polyurethane elastomers, polyurea elastomers,metallocene-catalyzed elastomers and plastomers, copolymers ofisobutylene and p-alkylstyrene, halogenated copolymers of isobutyleneand p-alkylstyrene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and blends of two or morethereof.

Preferably, the rubber composition comprises polybutadiene. In general,polybutadiene is a homopolymer of 1, 3-butadiene. The double bonds inthe 1, 3-butadiene monomer are attacked by catalysts to grow the polymerchain and form a polybutadiene polymer having a desired molecularweight. Any suitable catalyst may be used to synthesize thepolybutadiene rubber depending upon the desired properties. Normally, atransition metal complex (for example, neodymium, nickel, or cobalt) oran alkyl metal such as alkyllithium is used as a catalyst. Othercatalysts include, but are not limited to, aluminum, boron, lithium,titanium, and combinations thereof. The catalysts produce polybutadienerubbers having different chemical structures. In a cis-bondconfiguration, the main internal polymer chain of the polybutadieneappears on the same side of the carbon-carbon double bond contained inthe polybutadiene. In a trans-bond configuration, the main internalpolymer chain is on opposite sides of the internal carbon-carbon doublebond in the polybutadiene. The polybutadiene rubber can have variouscombinations of cis- and trans-bond structures. A preferredpolybutadiene rubber has a 1, 4 cis-bond content of at least 40%,preferably greater than 80%, and more preferably greater than 90%. Ingeneral, polybutadiene rubbers having a high 1, 4 cis-bond content havehigh tensile strength. The polybutadiene rubber may have a relativelyhigh or low Mooney viscosity.

Examples of commercially available polybutadiene rubbers that can beused in accordance with this invention, include, but are not limited to,BR 01 and BR 1220, available from BST Elastomers of Bangkok, Thailand;SE BR 1220LA and SE BR1203, available from DOW Chemical Co of Midland,Michigan; BUDENE 1207, 1207s, 1208, and 1280 available from Goodyear,Inc of Akron, Ohio; BR 01, 51 and 730, available from Japan SyntheticRubber (JSR) of Tokyo, Japan; BUNA CB 21, CB 22, CB 23, CB 24, CB 25, CB29 MES, CB 60, CB Nd 60, CB 55 NF, CB 70 B, CB KA 8967, and CB 1221,available from Lanxess Corp. of Pittsburgh. Pennsylvania; BR1208,available from LG Chemical of Seoul, South Korea; UBEPOL BR130B, BR150,BR150B, BR150L, BR230, BR360L, BR710, and VCR617, available from UBEIndustries, Ltd. of Tokyo, Japan; EUROPRENE NEOCIS BR 60, INTENE 60 AFand P3OAF, and EUROPRENE BR HV80, available from Polimeri Europa ofRome, Italy; AFDENE 50 and NEODENE BR40, BR45, BR50 and BR60, availablefrom Karbochem (PTY) Ltd. of Bruma, South Africa; KBR 01, NdBr 40,NdBR-45, NdBr 60, KBR 710S, KBR 710H, and KBR 750, available from KumhoPetrochemical Co., Ltd. of Seoul, South Korea; and DIENE 55NF, 70AC, and320 AC, available from Firestone Polymers of Akron, Ohio.

The polybutadiene rubber is used in an amount of at least about 5% byweight based on total weight of composition and is generally present inan amount of about 5% to about 100%, or an amount within a range havinga lower limit of 5% or 10% or 20% or 30% or 40% or 50% and an upperlimit of 55% or 60% or 70% or 80% or 90% or 95% or 100%. Preferably, theconcentration of polybutadiene rubber is about 40 to about 95 weightpercent. If desirable, lesser amounts of other thermoset materials maybe incorporated into the base rubber. Such materials include the rubbersdiscussed above, for example, cis-polyisoprene, trans-polyisoprene,balata, polychloroprene, polynorbornene, polyoctenamer, polypentenamer,butyl rubber, EPR, EPDM, styrene-butadiene, and the like. In otherversions, polybutadiene rubber is not used to form the polymeric matrix.Rather, a different thermoset rubber material is used. The curingmechanism for the thermoset rubber materials is described further below.

As discussed above, the thermoset or thermoplastic composition used toform the inner core contains a metal material. In one version, the metalmaterial can constitute the entire inner core. That is, the metalmaterial comprises 100% of the composition used to make the inner core.The metal material is preferably in the shape of a solid sphere, forexample, a ball bearing. The metal sphere can be used as the inner core(center) and a polymeric outer core layer can be disposed about themetal center. Alternatively, metal fillers, as described further below,can be dispersed in the polymeric binder to form a metal-containingcomposition that can be used to make the inner core. Relativelyheavy-weight metal materials such as, for example, a metal selected fromthe group consisting of copper, nickel, tungsten, brass, steel,magnesium, molybdenum, cobalt, lead, tin, silver, gold and platinumalloys can be used. Suitable steel materials include, for example,chrome steel, stainless steel, carbon steel, and alloys thereof.Alternatively, or in addition to the heavy metals, relativelylight-weight metal materials such as titanium and aluminum alloys can beused, provided the inner core layer has the required specific gravity.The metal filler is added to the composition in a sufficient amount toobtain the desired specific gravity as discussed further below.

If the size of the inner core (center) is small and a dense metalmaterial such as tungsten is being used, then the amount of tungstenneeded to obtain the desired specific gravity will be relatively low.The weight of such a dense metal material is more concentrated so asmaller amount of material is needed. On the other hand, if a lowdensity metal material such as aluminum is being used, then the amountof aluminum needed to reach the needed specific gravity will berelatively high. Normally, the metal filler is present in thecomposition in a concentration within the range of about 1% to about60%. Preferably, the metal filler is present in the composition in anamount of 20 wt. % or less, 15 wt % or less, or 12 wt % or less, or 10wt % or less, or 6 wt % or less, or 4 wt % or less based on weight ofpolymer in the composition.

The overall specific gravity of the core structure (inner core and outercore layers) is preferably at least 1.8 g/cc, more preferably at least2.00 g/cc, and most preferably at least 2.50 g/cc. In general, the innercore has a specific gravity of at least about 1.00 g/cc and is generallywithin the range of about 1.00 to about 20.00. Preferably, the innercore has a lower limit of specific gravity of about 1.10 or 1.20 or 1.50or 1.6 or 1.9 or 2.00 or 2.30 or 2.50 or 2.6 or 3.50 or 4.00 or 5.00 or5.60 or 6.00 or 6.20 or 6.80 or 7.00 or 7.40 or 8.00 g/cc and an upperlimit of about 9.00 or 9.50 or 10.00 or 10.50 or 11.00 or 11.20 or 12.00or 12.60 or 13.00 or 13.40 or 14. 00 or 14.50 or 15.00 or 16.00 or 16.40or 17.00 or 18.00 or 19.00 or 19.50g/cc. In a preferred embodiment, theinner core has a specific gravity of about 1.00 to about 14.00 g/cc,more preferably about 1.90 to about 13.50 g/cc.

Meanwhile, the outer core layer preferably has a relatively low specificgravity. Thus, the specific gravity of inner core layer (SG_(inner)) ispreferably greater than the specific gravity of inner, the outer corelayer (SG_(outer)). For example, the outer core layer may have aspecific gravity within a range having a lower limit of about 0.60 or 80or 0.90 or 1.00 or 1.25 or 2.00 or 2.50 or 3.00 or 3.50 or 4.00, 4.25 or5.00 and an upper limit of about 6.00 or 6.50 or 7.00 or 7.25 or 8.00 or8.50 or 9.00 or 9.25 or 10.00 g/cc. In one preferred embodiment, theSG_(inner) is preferably greater than the SG_(outer) by at least 0.5,more preferably 0.75 or greater, and more preferably 1.00 or greater. Inone embodiment, the difference between the SG_(inner) and SG_(outer) iswithin the range of about 0.5 to about 12.0. More particularly, thedifference between the SG_(inner) andd SG_(outer) can be 6.0 or greaterand within the range of about 6.0 to about 12.0.

Suitable metal fillers that can be added to the polymeric matrix used toform the inner core preferably have specific gravity values in the rangefrom about 1.5 to about 19.5, and include, for example, metal (or metalalloy) powder, metal oxide, metal stearates, particulates, flakes, andthe like, and blends thereof. Examples of useful metal (or metal alloy)powders include, but are not limited to, bismuth powder, boron powder,brass powder, bronze powder, cobalt powder, copper powder, iron powder,molybdenum powder, nickel powder, stainless steel powder, titanium metalpowder, zirconium oxide powder, aluminum flakes, tungsten metal powder,beryllium metal powder, zinc metal powder, or tin metal powder. Examplesof metal oxides include, but are not limited to, zinc oxide, iron oxide,aluminum oxide, titanium dioxide, magnesium oxide, zirconium oxide, andtungsten trioxide.

Plasticizers

The thermoset and thermoplastic compositions of this invention used tomake the inner core may contain a plasticizer. Plasticizers also can beadded to the compositions used to make the outer core. Adding theplasticizers helps to reduce the glass transition temperature (Tg) ofthe composition. The glass transition in a polymer is a temperaturerange below which a polymer is relatively brittle and above which it isrubber-like. In addition to lowering the Tg, the plasticizer may alsoreduce the tans in the temperature range above the Tg. The Tg of apolymer is measured by a Differential Scanning calorimeter or a DynamicMechanical Analyzer (DMA) and the DMA is used to measure tans. Theplasticizer may also reduce the hardness and compression of thecomposition when compared to its non-plasticized condition. The effectsof adding a plasticizer to the composition on Tg, flex modulus,hardness, and other physical properties are discussed further below.

The compositions may contain one or more plasticizers. The plasticizersthat may be used in the thermoplastic compositions of this inventioninclude, for example, N-butylbenzenesulfonamide (BBSA);N-ethylbenzenesulfonamide (EBSA); N-propylbenzenesulfonamide (PBSA);N-butyl-N-dodecylbenzenesulfonamide (BDBSA);N,N-dimethylbenzenesulfonamide (DMBSA); p-methylbenzenesulfonamide;o,p-toluene sulfonamide; p-toluene sulfonamide;2-ethylhexyl-4-hydroxybenzoate; hexadecyl-4-hydroxybenzoate;1-butyl-4-hydroxybenzoate; dioctyl phthalate; diisodecyl phthalate;di-(2-ethylhexyl) adipate; and tri-(2-ethylhexyl) phosphate.

In one preferred version, the plasticizer is selected from the group ofpolytetramethylene ether glycol (available from BASF under thetradename, PolyTHF™ 250); propylene carbonate (available from HuntsmanCorp., under the tradename, Jeffsol™ PC); and/or dipropyleneglycoldibenzoate (available from Eastman Chemical under the tradename,Benzoflex™ 284). Mixtures of these plasticizers also may be used.

Other suitable plasticizer compounds include benzene mono-, di-, andtricarboxylic acid esters. Phthalates such as Bis(2-ethylhexyl)phthalate (DEHP), Diisononyl phthalate (DINP), Di-n-butyl phthalate(DnBP, DBP), Butyl benzyl phthalate (BBP), Diisodecyl phthalate (DIDP),Dioctyl phthalate (DnOP), Diisooctyl phthalate (DIOP), Diethyl phthalate(DEP), Diisobutyl phthalate (DIBP), and Di-n-hexyl phthalate aresuitable. Iso- and terephthalates such as Dioctyl terephthalate andDinonyl isophthalate may be used. Also appropriate are trimellitatessuch as Trimethyl trimellitate (TMTM),Tri-(2-ethylhexyl) trimellitate(TOTM),Tri-(n-octyl,n-decyl) trimellitate , Tri-(heptyl,nonyl)trimellitate, Tri-n-octyl trimellitate; as well as benzoates, including:2-ethylhexyl-4-hydroxy benzoate, n-octyl benzoate, methyl benzoate, andethyl benzoate.

Also suitable are alkyl diacid esters commonly based on C4-C12 alkyldicarboxylic acids such as adipic, sebacic, azelaic, and maleic acidssuch as: Bis(2-ethylhexyl)adipate (DEHA), Dimethyl adipate (DMAD),Monomethyl adipate (MMAD), Dioctyl adipate (DOA), Dibutyl sebacate(DBS), Dibutyl maleate (DBM), Diisobutyl maleate (DIBM), Dioctylsebacate (DOS). Also, esters based on glycols, polyglycols andpolyhydric alcohols such as poly(ethylene glycol) mono- and di-esters,cyclohexanedimethanol esters, sorbitol derivatives; and triethyleneglycol dihexanoate, diethylene glycol di-2-ethylhexanoate, tetraethyleneglycol diheptanoate, and ethylene glycol dioleate may be used.

Fatty acids, fatty acid salts, fatty acid amides, and fatty acid estersalso may be used in the compositions of this invention. Compounds suchas stearic, oleic, ricinoleic, behenic, myristic, linoleic, palmitic,and lauric acid esters, salts, and mono- and bis-amides can be used.Ethyl oleate, butyl stearate, methyl acetylricinoleate, zinc oleate,ethylene bis-oleamide, and stearyl erucamide are suitable. Suitablefatty acid salts include, for example, metal stearates, erucates,laurates, oleates, palmitates, pelargonates, and the like. For example,fatty acid salts such as zinc stearate, calcium stearate, magnesiumstearate, barium stearate, and the like can be used. Fatty alcohols andacetylated fatty alcohols are also suitable, as are carbonate esterssuch as propylene carbonate and ethylene carbonate. In a particularlypreferred version, the fatty acid ester, ethyl oleate is used as theplasticizer.

Glycerol-based esters such as soy-bean, tung, or linseed oils or theirepoxidized derivatives can also be used as plasticizers in the presentinvention, as can polymeric polyester plasticizers formed from theesterification reaction of diacids and diglycols as well as from thering-opening polymerization reaction of caprolactones with diacids ordiglycols. Citrate esters and acetylated citrate esters are alsosuitable. Glycerol mono-, di-, and tri-oleates may be used per thisinvention, and in one preferred embodiment, glycerol trioleate is usedas the plasticizer.

Dicarboxylic acid molecules containing both a carboxylic acid ester anda carboxylic acid salt can perform suitably as plasticizers. Themagnesium salt of mono-methyl adipate and the zinc salt of mono-octylglutarate are two such examples for this invention. Tri- andtetra-carboxylic acid esters and salts can also be used.

Also envisioned as suitable plasticizers are organophosphate andorganosulfur compounds such as tricresyl phosphate (TCP), tributylphosphate(TBP), alkyl sulfonic acid phenyl esters (ASE); andsulfonamides such as N-ethyl toluene sulfonamide,N-(2-hydroxypropyl)benzene sulfonamide, N-(n-butyl) benzene sulfonamide. Furthermore,thioester and thioether variants of the plasticizer compounds mentionedabove are suitable.

Non-ester plasticizers such as alcohols, polyhydric alcohols, glycols,polyglycols, and polyethers also are suitable materials forplasticization. Materials such as polytetramethylene ether glycol,poly(ethylene glycol), and poly(propylene glycol), ( )eyl alchohol, andcetyl alcohol can be used. Hydrocarbon compounds, both saturated andunsaturated, linear or cyclic can be used such as mineral oils,microcrystalline waxes, or low-molecular weight polybutadiene.Halogenated hydrocarbon compounds can also be used.

Other examples of plasticizers that may be used in the composition ofthis invention include butylbenzenesulphonamide (BBSA), ethylhexylpara-hydroxybenzoate (EHPB) and decylhexyl para-hydroxybenzoate (DHPB),as disclosed in Montanari et al., U.S. Pat. No. 6,376,037, thedisclosure of which is hereby incorporated by reference.

Esters and alkylamides such as phthalic acid esters including dimethylphthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate,di-2-ethylhexyl phthalate, di-n-octyl phthalate, diisodecyl phthalate,ditridecyl phthalate, dicyclohexyl phthalate, butylbenzyl phthalate,diisononyl phthalate, ethylphthalylethyl glycolate, butylphthalylbutylglycolate, diundecyl phthalate, di-2-ethylhexyl tetrahydrophthalate asdisclosed in Isobe et al., U.S. Pat. No. 6,538,099, the disclosure ofwhich is hereby incorporated by reference, also may be used.

Jacques et al., U.S. Pat. No. 7,045,185, the disclosure of which ishereby incorporated by reference, discloses sulphonamides such asN-butylbenzenesulphonamide, ethyltoluene-suiphonamide,N-cyclohexyltoluenesulphonamide, 2-ethylhexyl-para-hydroxybenzoate,2-decylhexyl-para-hydroxybenzoate, oligoethyleneoxytetrahydrofurfurylalcohol, or oligoethyleneoxy malonate; esters of hydroxybenzoic acid;esters or ethers of tetrahydrofurfuryl alcohol, and esters of citricacid or hydroxymalonic acid; and these plasticizers also may be used.

Sulfonamides also may be used in the present invention, and thesematerials are described in Fish, Jr. et al., U.S. Pat. No. 7,297,737,the disclosure of which is hereby incorporated by reference. Examples ofsuch sulfonamides include N-alkyl benzenesulfonamides andtoluenesufonamides, particularly N-butylbenzenesulfonamide,N-(2-hydroxypropyl)benzenesulfonamide, N-ethyl-o-toluenesulfonamide,N-ethyl-p-toluenesulfonamide, o-toluenesulfonamide, p-toluenesulfonamide. Such sulfonamide plasticizers also are described in Hochstetter etal., US Patent Application Publication 2010/0183837, the disclosure ofwhich is hereby incorporated by reference.

As noted above, the fatty acid esters are particularly preferredplasticizers in the present invention. It has been found that the fattyacid esters perform well as plasticizers in ethylene acid copolymercompositions. The fatty acid esters have several advantageousproperties. For example, the fatty acid esters are compatible with theethylene acid copolymers and they tend to blend uniformly and completelywith the acid copolymer. Also, the fatty acid esters tend to improve theresiliency and/or compression of the composition as discussed furtherbelow. The ethylene acid copolymer/plasticizer compositions may containother ingredients that do not materially affect the basic and novelcharacteristics of the composition. For example, mineral fillers may beadded as discussed above. In one particular version, the compositionconsists essentially of ethylene acid copolymer, metal, and plasticizer,particularly a fatty acid ester. In another particular version, thecomposition consists essentially of ethylene acid copolymer, cationsource sufficient to neutralize at least 20% of the acid groups presentin the composition, metal, and plasticizer, particularly a fatty acidester.

One method of preparing the fatty acid ester involves reacting the fattyacid or mixture of fatty acids with a corresponding alcohol. The alcoholcan be any alcohol including, but not limited to, linear, branched, andcyclic alcohols. The fatty acid ester is commonly a methyl, ethyl,n-propyl, or butyl ester of a carboxylic acid that contains from 4 to 30carbon atoms. In the present invention, ethyl esters and particularlyethyl oleate are preferred fatty acid esters because of theirproperties. The carboxylic acid may be saturated or unsaturated.Examples of suitable saturated carboxylic acids, that is, carboxylicacids in which the carbon atoms of the alkyl chain are connected bysingle bonds, include but are not limited to butyric acid (chain lengthof C₄ and molecular weight of 88.1); capric acid (C₁₀ and MW of 172.3);lauric acid (C₁₂ and MW of 200.3); myristic acid (C₁₄ and MW of 228.4);palmitic acid (C₁₆ and MW of 256.4); stearic acid (C₁₈ and MW of 284.5);and behenic acid (C₂₂ and MW of 340.6). Examples of suitable unsaturatedcarboxylic acids, that is, a carboxylic acid in which there is one ormore double bonds between the carbon atoms in the alkyl chain, includebut are not limited to oleic acid (chain length and unsaturation C18:1;and MW of 282.5); linoleic acid (C18:2 and MW of 280.5; linolenic acid(C18:3 and MW of 278.4); and erucic acid (C22:1 and MW of 338.6).

It is believed that the plasticizer should be added in a sufficientamount to the composition so there is a substantial change in thestiffness and/or hardness of the composition. Thus, although theconcentration of plasticizer may be as little as 1% by weight to formsome compositions per this invention, it is preferred that theconcentration be relatively greater. For example, it is preferred thatthe concentration of the plasticizer be at least 3 weight percent (wt.%). More particularly, it is preferred that the plasticizer be presentin an amount within a range having a lower limit of 1% or 3% or 5% or 7%or 8% or 10% or 12% or 15% or 18% and an upper limit of 20% or 22% or25% or 30% or 35% or 40% or 42% or 50% or 55% or 60% or 66% or 71% or75% or 80%. In one preferred embodiment, the concentration ofplasticizer falls within the range of about 7% to about 75%, preferablyabout 9% to about 55%, and more preferably about 15% to about 50%.

Outer Core Composition

As discussed above, the inner core (center) may be formed frommetal-containing, thermoset or thermoplastic compositions. Likewise, theouter core layer may be formed from thermoset or thermoplasticmaterials. A plasticizer, as described above, optionally may be added tothe thermoset or thermoplastic composition used to form the outer corelayer. In one particularly preferred embodiment, the outer core layer isformed from a thermoset rubber composition. Thus, in one preferredversion, the inner core is formed from a metal-containing, thermoplasticcomposition and the outer core is formed from a thermoset composition.In another version, the inner core is formed from a metal-containing,thermoset composition, and the outer core is formed from a thermosetcomposition. More particularly, the inner core is formed from a firstmetal-containing, thermoset composition and the outer core layer isformed from a second thermoset composition. The same or differentingredients may be used to form the first and second thermosetcompositions, respectively. However, the second thermoplasticcomposition preferably has different hardness and flex modulus valuesthan the first thermoplastic composition. Suitable thermoplasticmaterials that can be used to make the inner and outer core layers aredescribed further below.

Preferably, an ionomer composition comprising an ethylene acid copolymercontaining acid groups that are at least partially neutralized is usedto form the thermoplastic composition. As discussed above, thethermoplastic composition can be used to form the inner or outer corelayer. In one embodiment, the neutralization level of the ethylene acidcopolymer is greater than 70%. For example, the neutralization level maybe at least 90%, and even at least 100% in some instances.Alternatively, the neutralization level may be less than 70%.Preferably, a highly neutralized polymer (HNP) is used to form thethermoplastic composition as discussed further below.

Suitable ethylene acid copolymers that may be used to form therespective compositions of this invention are generally referred to ascopolymers of ethylene; C₃ to C₈ α, β-ethylenically unsaturated mono-ordicarboxylic acid; and optional softening monomer. Copolymers mayinclude, without limitation, ethylene acid copolymers, such asethylene/(meth)acrylic acid, ethylene/(meth)acrylic acid/maleicanhydride, ethylene/(meth)acrylic acid/maleic acid mono-ester,ethylene/maleic acid, ethylene/maleic acid mono-ester,ethylene/(meth)acrylic acid/n-butyl (meth)acrylate,ethylene/(meth)acrylic acid/iso-butyl (meth)acrylate,ethylene/(meth)acrylic acid/methyl (meth)acrylate,ethylene/(meth)acrylic acid/ethyl (meth)acrylate terpolymers, and thelike. The term, “copolymer,” as used herein, includes polymers havingtwo types of monomers, those having three types of monomers, and thosehaving more than three types of monomers. Preferred α, β-ethylenicallyunsaturated mono- or dicarboxylic acids are (meth) acrylic acid,ethacrylic acid, maleic acid, crotonic acid, fumaric acid, itaconicacid. (Meth) acrylic acid is most preferred. As used herein, “(meth)acrylic acid” means methacrylic acid and/or acrylic acid. Likewise,“(meth) acrylate” means methacrylate and/or acrylate.

When a softening monomer is included, such copolymers are referred toherein as E/X/Y-type copolymers, wherein E is ethylene; X is a C₃ to C₈α, β-ethylenically unsaturated mono- or dicarboxylic acid; and Y is asoftening monomer. The softening monomer is typically an alkyl (meth)acrylate, wherein the alkyl groups have from 1 to 8 carbon atoms.Preferred E/X/Y-type copolymers are those wherein X is (meth) acrylicacid and/or Y is selected from (meth) acrylate, n-butyl (meth) acrylate,isobutyl (meth) acrylate, methyl (meth) acrylate, and ethyl (meth)acrylate. More preferred E/X/Y-type copolymers are ethylene/(meth)acrylic acid/n-butyl acrylate, ethylene/(meth) acrylic acid/methylacrylate, and ethylene/(meth) acrylic acid/ethyl acrylate.

The amount of ethylene in the acid copolymer is typically at least 15wt. %, preferably at least 25 wt. %, more preferably least 40 wt. %, andeven more preferably at least 60 wt. %, based on total weight of thecopolymer. The amount of C₃ to C₈ α, β-ethylenically unsaturated mono-or dicarboxylic acid in the acid copolymer is typically from 1 wt. % to35 wt. %, preferably from 5 wt. % to 30 wt. %, more preferably from 5wt. % to 25 wt. %, and even more preferably from 10 wt. % to 20 wt. %,based on total weight of the copolymer. The amount of optional softeningcomonomer in the acid copolymer is typically from 0 wt. % to 50 wt. %,preferably from 5 wt. % to 40 wt. %, more preferably from 10 wt. % to 35wt. %, and even more preferably from 20 wt. % to 30 wt. %, based ontotal weight of the copolymer. “Low acid” and “high acid” ionomericpolymers, as well as blends of such ionomers, may be used. In general,low acid ionomers are considered to be those containing 16 wt. % or lessof acid moieties, whereas high acid ionomers are considered to be thosecontaining greater than 16 wt. % of acid moieties.

The acidic groups in the copolymeric ionomers are partially or totallyneutralized with a cation source. Suitable cation sources include metalcations and salts thereof, organic amine compounds, ammonium, andcombinations thereof. Preferred cation sources are metal cations andsalts thereof, wherein the metal is preferably lithium, sodium,potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum,manganese, nickel, chromium, copper, or a combination thereof. The metalcation salts provide the cations capable of neutralizing (at varyinglevels) the carboxylic acids of the ethylene acid copolymer and fattyacids, if present, as discussed further below. These include, forexample, the sulfate, carbonate, acetate, oxide, or hydroxide salts oflithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc,aluminum, manganese, nickel, chromium, copper, or a combination thereof.Preferred metal cation salts are calcium and magnesium-based salts. Highsurface area cation particles such as micro and nano-scale cationparticles are preferred. The amount of cation used in the composition isreadily determined based on desired level of neutralization.

For example, ionomeric resins having acid groups that are neutralizedfrom about 10 percent to about 100 percent may be used. In one ionomercomposition, the acid groups are partially neutralized. That is, theneutralization level is from about 10% to about 70%, more preferably 20%to 60%, and most preferably 30 to 50%. These ionomer compositions,containing acid groups neutralized to 70% or less, may be referred toionomers having relatively low neutralization levels.

On the other hand, the ionomer composition may contain acid groups thatare highly or fully-neutralized. These highly neutralized polymers(HNPs) are preferred for forming at least one core layer in the presentinvention and are discussed in further detail below. In these HNPs, theneutralization level is greater than 70%, preferably at least 90% andeven more preferably at least 100%. In another embodiment, an excessamount of neutralizing agent, that is, an amount greater than thestoichiometric amount needed to neutralize the acid groups, may be used.That is, the acid groups may be neutralized to 100% or greater, forexample 110% or 120% or greater. In one preferred embodiment, a highacid ethylene acid copolymer containing about 19 to 20 wt. % methacrylicor acrylic acid is neutralized with zinc and sodium cations to a 95%neutralization level.

Highly Neutralized Polymer (HNP) Compositions

Suitable highly-neutralized polymer (HNP) compositions comprise an HNPand optionally melt-flow modifier(s), additive(s), and/or filler(s).When used to form the inner core, the HNP composition also containsmetal materials as discussed above. For purposes of the presentdisclosure, “HNP” refers to an acid polymer after at least 70%,preferably at least 80%, more preferably at least 90%, more preferablyat least 95%, and even more preferably 100%, of the acid groups presentare neutralized. It is understood that the HNP may be a blend of two ormore HNPs. Preferred acid polymers are copolymers of an α-olefin and aC₃-C₈α,β-ethylenically unsaturated carboxylic acid, optionally includinga softening monomer. The α-olefin is preferably selected from ethyleneand propylene. The acid is preferably selected from (meth) acrylic acid,ethacrylic acid, maleic acid, crotonic acid, fumaric acid, and itaconicacid. (Meth) acrylic acid is particularly preferred. The optionalsoftening monomer is preferably selected from alkyl (meth) acrylate,wherein the alkyl groups have from 1 to 8 carbon atoms. Preferred acidpolymers include, but are not limited to, those wherein the α-olefin isethylene, the acid is (meth) acrylic acid, and the optional softeningmonomer is selected from (meth) acrylate, n-butyl (meth) acrylate,isobutyl (meth) acrylate, methyl (meth) acrylate, and ethyl (meth)acrylate. Particularly preferred acid polymers include, but are notlimited to, ethylene/(meth) acrylic acid/n-butyl acrylate,ethylene/(meth) acrylic acid/methyl acrylate, and ethylene/(meth)acrylic acid/ethyl acrylate.

Suitable acid polymers for forming the HNP also include acid polymersthat are already partially neutralized. Examples of suitable partiallyneutralized acid polymers include, but are not limited to, Surlyn®ionomers, commercially available from E. I. du Pont de Nemours andCompany; AClyn® ionomers, commercially available from HoneywellInternational Inc.; and lotek® ionomers, commercially available fromExxonMobil Chemical Company. Also suitable are DuPont® HPF 1000 andDuPont® HPF 2000, ionomeric materials commercially available from E. I.du Pont de Nemours and Company. In some embodiments, very low modulusionomer-(“VLMI-”) type ethylene-acid polymers are particularly suitablefor forming the HNP, such as Surlyn® 6320, Surlyn® 8120, Surlyn® 8320,and Surlyn® 9320, commercially available from E. I. du Pont de Nemoursand Company.

The α-olefin is typically present in the acid polymer in an amount of 15wt % or greater, or 25 wt % or greater, or 40 wt % or greater, or 60 wt% or greater, based on the total weight of the acid polymer. The acid istypically present in the acid polymer in an amount within a range havinga lower limit of 1 or 2 or 4 or 6 or 8 or 10 or 12 or 15 or 16 or 20 wt% and an upper limit of 20 or 25 or 26 or 30 or 35 or 40 wt %, based onthe total weight of the acid polymer. The optional softening monomer istypically present in the acid polymer in an amount within a range havinga lower limit of 0 or 1 or 3 or 5 or 11 or 15 or 20 wt % and an upperlimit of 23 or 25 or 30 or 35 or 50 wt %, based on the total weight ofthe acid polymer.

Additional suitable acid polymers are more fully described, for example,in U.S. Pat. Nos. 5,691,418, 6,562,906, 6,653,382, 6,777,472, 6,762,246,6,815,480, and 6,953,820 and U.S. Patent Application Publication Nos.2005/0148725, 2005/0049367, 2005/0020741, 2004/0220343, and2003/0130434, the entire disclosures of which are hereby incorporatedherein by reference.

The HNP is formed by reacting the acid polymer with a sufficient amountof cation source, optionally in the presence of a high molecular weightorganic acid or salt thereof, such that at least 70%, preferably atleast 80%, more preferably at least 90%, more preferably at least 95%,and even more preferably 100%, of all acid groups present areneutralized. In a particular embodiment, the cation source is present inan amount sufficient to neutralize, theoretically, greater than 100%, or105% or greater, or 110% or greater, or 115% or greater, or 120% orgreater, or 125% or greater, or 200% or greater, or 250% or greater ofall acid groups present in the composition. The acid polymer can bereacted with the optional high molecular weight organic acid or saltthereof and the cation source simultaneously, or the acid polymer can bereacted with the optional high molecular weight organic acid or saltthereof prior to the addition of the cation source.

Suitable cation sources include metal ions and compounds of alkalimetals, alkaline earth metals, and transition metals; metal ions andcompounds of rare earth elements; and combinations thereof. Preferredcation sources are metal ions and compounds of magnesium, sodium,potassium, cesium, calcium, barium, manganese, copper, zinc, tin,lithium, and rare earth metals. The acid polymer may be at leastpartially neutralized prior to contacting the acid polymer with thecation source to form the HNP. Methods of preparing ionomers, and theacid polymers on which ionomers are based, are disclosed, for example,in U.S. Pat. Nos. 3,264,272, and 4,351,931, and U.S. Patent ApplicationPublication No. 2002/0013413.

Suitable high molecular weight organic acids, for both the metal saltand as a component of the ester plasticizer, are aliphatic organicacids, aromatic organic acids, saturated monofunctional organic acids,unsaturated monofunctional organic acids, multi-unsaturatedmonofunctional organic acids, and dimerized derivatives thereof.Particular examples of suitable organic acids include, but are notlimited to, caproic acid, caprylic acid, capric acid, lauric acid,stearic acid, behenic acid, erucic acid, oleic acid, linoleic acid,myristic acid, benzoic acid, palmitic acid, phenylacetic acid,naphthalenoic acid, dimerized derivatives thereof, and combinationsthereof. Salts of high molecular weight organic acids comprise thesalts, particularly the barium, lithium, sodium, zinc, bismuth,chromium, cobalt, copper, potassium, strontium, titanium, tungsten,magnesium, and calcium salts, of aliphatic organic acids, aromaticorganic acids, saturated monofunctional organic acids, unsaturatedmonofunctional organic acids, multi-unsaturated monofunctional organicacids, dimerized derivatives thereof, and combinations thereof. Suitableorganic acids and salts thereof are more fully described, for example,in U.S. Pat. No. 6,756,436, the entire disclosure of which is herebyincorporated herein by reference. In a particular embodiment, the HNPcomposition comprises an organic acid salt in an amount of 20 phr orgreater, or 25 phr or greater, or 30 phr or greater, or 35 phr orgreater, or 40 phr or greater.

The HNP compositions of the present invention optionally contain one ormore melt-flow modifiers. The amount of melt-flow modifier in thecomposition is readily determined such that the melt-flow index of thecomposition is at least 0.1 g/10 min, preferably from 0.5 g/10 min to10.0 g/10 min, and more preferably from 1.0 g/10 min to 6.0 g/10 min, asmeasured using ASTM D-1238, condition E, at 190° C., using a 2160 gramweight.

It is not required that a conventional melt-flow modifier be added tothe HNP composition of this invention. Such melt-flow modifiers areoptional. If a melt-flow modifier is added, it may be selected from thegroup of traditional melt-flow modifiers including, but not limited to,the high molecular weight organic acids and salts thereof disclosedabove, polyamides, polyesters, polyacrylates, polyurethanes, polyethers,polyureas, polyhydric alcohols, and combinations thereof. Also suitableare the non-fatty acid melt-flow modifiers disclosed in U.S. Pat. Nos.7,365,128 and 7,402,629, the entire disclosures of which are herebyincorporated herein by reference. However, as discussed above, certainplasticizers are added to the composition of this invention, and it isrecognized that such plasticizers may modify the melt-flow of thecomposition in some instances.

The HNP compositions of the present invention optionally includeadditive(s) and/or filler(s) in an amount within a range having a lowerlimit of 0 or 5 or 10 wt %, and an upper limit of 15 or 20 or 25 or 30or 50 wt %, based on the total weight of the composition. Suitableadditives and fillers include, but are not limited to, chemical blowingand foaming agents, optical brighteners, coloring agents, fluorescentagents, whitening agents, UV absorbers, light stabilizers, defoamingagents, processing aids, mica, talc, nano-fillers, antioxidants,stabilizers, softening agents, fragrance components, impact modifiers,TiO₂, acid copolymer wax, surfactants, and fillers, such as zinc oxide,tin oxide, barium sulfate, zinc sulfate, calcium oxide, calciumcarbonate, zinc carbonate, barium carbonate, clay, tungsten, tungstencarbide, silica, lead silicate, regrind (recycled material), andmixtures thereof. Suitable additives are more fully disclosed, forexample, in U.S. Patent Application Publication No. 2003/0225197, theentire disclosure of which is hereby incorporated herein by reference.

In some embodiments, the HNP composition is a “moisture resistant” HNPcomposition, i.e., having a moisture vapor transmission rate (“MVTR”) of8 g-mil/100 in²/day or less (i.e., 3.2 g-mm/m²·day or less), or 5g-mil/100 in²/day or less (i.e., 2.0 g-mm/m²·day or less), or 3g-mil/100 in²/day or less (i.e., 1.2 g-mm/m²·day or less), or 2g-mil/100 in²/day or less (i.e., 0.8 g-mm/m²·day or less), or 1g-mil/100 in²/day or less (i.e., 0.4 g-mm/m²·day or less), or less than1 g-mil/100 in²/day (i.e., less than 0.4 g-mm/m²·day). Suitable moistureresistant HNP compositions are disclosed, for example, in U.S. PatentApplication Publication Nos. 2005/0267240, 2006/0106175, and2006/0293464, the entire disclosures of which are hereby incorporatedherein by reference.

The HNP compositions of the present invention are not limited by anyparticular method or any particular equipment for making thecompositions. In a preferred embodiment, the composition is prepared bythe following process. The acid polymer(s), plasticizers, optionalmelt-flow modifier(s), and optional additive(s)/filler(s) aresimultaneously or individually fed into a melt extruder, such as asingle or twin screw extruder. Other suitable methods for incorporatingthe plasticizer into the composition are described further below. Asuitable amount of cation source is then added such that at least 70%,or at least 80%, or at least 90%, or at least 95%, or at least 100%, ofall acid groups present are neutralized. Optionally, the cation sourceis added in an amount sufficient to neutralize, theoretically, 105% orgreater, or 110% or greater, or 115% or greater, or 120% or greater, or125% or greater, or 200% or greater, or 250% or greater of all acidgroups present in the composition. The acid polymer may be at leastpartially neutralized prior to the above process. The components areintensively mixed prior to being extruded as a strand from the die-head.

The HNP composition optionally comprises at least one additional polymercomponent selected from partially neutralized ionomers as disclosed, forexample, in U.S. Patent Application Publication No. 2006/0128904, theentire disclosure of which is hereby incorporated herein by reference;bimodal ionomers, such as those disclosed in U.S. Patent ApplicationPublication No. 2004/0220343 and U.S. Pat. Nos. 6,562,906, 6,762,246,7,273,903, 8,193,283, 8,410,219, and 8,410,220, the entire disclosuresof which are hereby incorporated herein by reference, and particularlySurlyn® AD 1043, 1092, and 1022 ionomer resins, commercially availablefrom E. I. du Pont de Nemours and Company; ionomers modified withrosins, such as those disclosed in U.S. Patent Application PublicationNo. 2005/0020741, the entire disclosure of which is hereby incorporatedby reference; soft and resilient ethylene copolymers, such as thosedisclosed U.S. Patent Application Publication No. 2003/0114565, theentire disclosure of which is hereby incorporated herein by reference;polyolefins, such as linear, branched, or cyclic, C₂-C₄₀ olefins,particularly polymers comprising ethylene or propylene copolymerizedwith one or more C₂-C₄₀ olefins, C₃-C₂₀ α-olefins, or C₃-C₁₀ α-olefins;polyamides; polyesters; polyethers; polycarbonates; polysulfones;polyacetals; polylactones; acrylonitrile-butadiene-styrene resins;polyphenylene oxide; polyphenylene sulfide; styrene-acrylonitrileresins; styrene maleic anhydride; polyimides; aromatic polyketones;ionomers and ionomeric precursors, acid copolymers, and conventionalHNPs, such as those disclosed in U.S. Pat. Nos. 6,756,436, 6,894,098,and 6,953,820, the entire disclosures of which are hereby incorporatedherein by reference; polyurethanes; grafted and non-graftedmetallocene-catalyzed polymers, such as single-site catalyst polymerizedpolymers, high crystalline acid polymers, cationic ionomers, andcombinations thereof.

Other polymer components that may be included in the HNP compositioninclude, for example, natural and synthetic rubbers, including, but notlimited to, ethylene propylene rubber (“EPR”), ethylene propylene dienerubber (“EPDM”), styrenic block copolymer rubbers (such as SI, SIS, SB,SBS, SIBS, and the like, where “S” is styrene, “I” is isobutylene, and“B” is butadiene), butyl rubber, halobutyl rubber, copolymers ofisobutylene and para-alkylstyrene, halogenated copolymers of isobutyleneand para-alkylstyrene, natural rubber, polyisoprene, copolymers ofbutadiene with acrylonitrile, polychloroprene, alkyl acrylate rubber(such as ethylene-alkyl acrylates and ethylene-alkyl methacrylates, and,more specifically, ethylene-ethyl acrylate, ethylene-methyl acrylate,and ethylene-butyl acrylate), chlorinated isoprene rubber, acrylonitrilechlorinated isoprene rubber, and polybutadiene rubber (cis and trans).Additional suitable blend polymers include those described in U.S. Pat.No. 5,981,658, for example at column 14, lines 30 to 56, the entiredisclosure of which is hereby incorporated herein by reference.

The blend may be produced by post-reactor blending, by connectingreactors in series to make reactor blends, or by using more than onecatalyst in the same reactor to produce multiple species of polymer. Thepolymers may be mixed prior to being put into an extruder, or they maybe mixed in an extruder. In a particular embodiment, the HNP compositioncomprises an acid copolymer and an additional polymer component, whereinthe additional polymer component is a non-acid polymer present in anamount of greater than 50 wt %, or an amount within a range having alower limit of 50 or 55 or 60 or 65 or 70 and an upper limit of 80 or 85or 90, based on the combined weight of the acid copolymer and thenon-acid polymer. In another particular embodiment, the HNP compositioncomprises an acid copolymer and an additional polymer component, whereinthe additional polymer component is a non-acid polymer present in anamount of less than 50 wt %, or an amount within a range having a lowerlimit of 10 or 15 or 20 or 25 or 30 and an upper limit of 40 or 45 or50, based on the combined weight of the acid copolymer and the non-acidpolymer.

The HNP compositions of the present invention, in the neat (i.e.,unfilled) form, preferably have a specific gravity of from 0.95 g/cc to0.99 g/cc. Any suitable filler, flake, fiber, particle, or the like, ofan organic or inorganic material may be added to the HNP composition toincrease or decrease the specific gravity, particularly to adjust theweight distribution within the golf ball, as further disclosed in U.S.Pat. Nos. 6,494,795, 6,547,677, 6,743,123, 7,074,137, and 6,688,991, theentire disclosures of which are hereby incorporated herein by reference.

Other suitable thermoplastic polymers that may be used to form the innerand outer core layers include, but are not limited to, the followingpolymers (including homopolymers, copolymers, and derivatives thereof):(a) polyesters, particularly those modified with a compatibilizing groupsuch as sulfonate or phosphonate, including modified poly(ethyleneterephthalate), modified poly(butylene terephthalate), modifiedpoly(propylene terephthalate), modified poly(trimethyleneterephthalate), modified poly(ethylene naphthenate), and those disclosedin U.S. Pat. Nos. 6,353,050, 6,274,298, and 6,001,930, the entiredisclosures of which are hereby incorporated herein by reference, andblends of two or more thereof; (b) polyamides, polyamide-ethers, andpolyamide-esters, and those disclosed in U.S. Pat. Nos. 6,187,864,6,001,930, and 5,981,654, the entire disclosures of which are herebyincorporated herein by reference, and blends of two or more thereof; (c)polyurethanes, polyureas, polyurethane-polyurea hybrids, and blends oftwo or more thereof; (d) fluoropolymers, such as those disclosed in U.S.Pat. Nos. 5,691,066, 6,747,110 and 7,009,002, the entire disclosures ofwhich are hereby incorporated herein by reference, and blends of two ormore thereof; (e) polystyrenes, such as poly(styrene-co-maleicanhydride), acrylonitrile-butadiene-styrene, poly(styrene sulfonate),polyethylene styrene, and blends of two or more thereof; (f) polyvinylchlorides and grafted polyvinyl chlorides, and blends of two or morethereof; (g) polycarbonates, blends ofpolycarbonate/acrylonitrile-butadiene-styrene, blends ofpolycarbonate/polyurethane, blends of polycarbonate/polyester, andblends of two or more thereof; (h) polyethers, such as polyaryleneethers, polyphenylene oxides, block copolymers of alkenyl aromatics withvinyl aromatics and polyamicesters, and blends of two or more thereof;(i) polyimides, polyetherketones, polyamideimides, and blends of two ormore thereof; and (j) polycarbonate/polyester copolymers and blends.

These thermoplastic polymers may be used by and in themselves to formthe inner and outer core layers, or blends of thermoplastic polymersincluding the above-described polymers and ethylene acid copolymerionomers may be used. It also is recognized that the ionomercompositions may contain a blend of two or more ionomers. For example,the composition may contain a 50/50 wt. % blend of two differenthighly-neutralized ethylene/methacrylic acid copolymers. In anotherversion, the composition may contain a blend of one or more ionomers anda maleic anhydride-grafted non-ionomeric polymer. The non-ionomericpolymer may be a metallocene-catalyzed polymer. In another version, thecomposition contains a blend of a highly-neutralizedethylene/methacrylic acid copolymer and a maleic anhydride-graftedmetallocene-catalyzed polyethylene. In yet another version, thecomposition contains a material selected from the group consisting ofhighly-neutralized ionomers optionally blended with a maleicanhydride-grafted non-ionomeric polymer; polyester elastomers; polyamideelastomers; and combinations of two or more thereof.

More particularly, in one version, the same thermoplastic compositionused to form the inner core also may be used to form the outer corelayer. Alternatively, in other versions, different thermoplasticcompositions are used to form the inner and outer core layers. Forexample, in one embodiment, the inner and outer core layers have thesame specific gravity levels. In a second embodiment, the specificgravity of the inner core is greater than the specific gravity of theouter core layer. Finally, in a third embodiment, the specific gravityof the inner core is less than the specific gravity of the outer corelayer. Thus, both the inner and outer core layers may be formed from anethylene acid copolymer ionomer composition, for example.

Specific Gravity of Layers

The respective thermoplastic and thermoset compositions used to make theinner core layers may contain metals as described above. Conventionaladditives, for example, those additives described below as beingsuitable for rubber formulations, also may be included in thethermoplastic composition. The amount and type of specific gravityfillers used in each layer, if any, may be adjusted to achieve a desiredspecific gravity. For example, if the objective is to make the specificgravities of the inner and outer core layers different, in one example,the inner core layer may contain a relatively small concentration ofmetal fillers, while the outer core layer may contain a largeconcentration of metal fillers. In another embodiment, the inner coreand/or outer core layer may not contain any metal materials. In yetanother example, the outer core layer may contain a small concentrationof metal fillers, while the inner core layer contains a largeconcentration of metal materials. On the other hand, if the objective isto make the specific gravities of the inner and outer core layerssubstantially the same, then the inner and outer core layers may containthe same concentration of metal fillers in the same polymeric matrix.

As discussed above, the specific gravity of inner core layer(SG_(inner)) is preferably greater inner, than the specific gravity ofthe outer core layer (SG_(outer)). In general, the specific gravities ofthe respective pieces of an object affect the Moment of Inertia (MOI) ofthe object. In general, the Moment of Inertia of a ball (or otherobject) about a given axis refers to how difficult it is to change theball's angular motion about that axis. If the ball's mass isconcentrated towards the center (the center piece has a higher specificgravity than the outer piece), less force is required to change itsrotational rate, and the ball has a relatively low Moment of Inertia. Insuch balls, most of the mass is located close to the ball's axis ofrotation and less force is needed to generate spin. Thus, the ball has agenerally high spin rate. Conversely, if the ball's mass is concentratedtowards the outer surface (the outer piece has a higher specific gravitythan the center piece), more force is required to change its rotationalrate, and the ball has a relatively high Moment of Inertia. That is, insuch balls, most of the mass is located away from the ball's axis ofrotation and more force is needed to generate spin. Such balls have agenerally low spin rate.

The golf balls of this invention having the above-described coreconstructions show both good resiliency and spin control. The resultingball has a relatively high Coefficient of Restitution (COR) allowing itto reach a high velocity when struck by a golf club. Thus, the balltends to travel a long distance and this is particularly important fordriver shots off the tee. At the same time, the ball has a soft touchand feel. Thus, the golfer has better control over the ball which isparticularly important when making approach shots using irons near thegreen. The golfer can hit the ball with a soft touch so that it dropsand stops quickly on the green. Furthermore, professional and highlyskilled recreational golfers can place a back-spin on the ball for evenbetter accuracy and shot-control. For such golfers, the right amount ofspin and touch can be placed on the ball easily. The ball is moreplayable and the golfer has more comfort playing with such a ball. Thegolfer can hit the ball so that it flies the correct distance whilemaintaining control over flight trajectory, spin, and placement.

More particularly, as described in Sullivan, U.S. Pat. No. 6,494,795 andLadd et al., U.S. Pat. No. 7,651,415, the formula for the Moment ofInertia for a sphere through any diameter is given in the CRC StandardMathematical Tables, 24th Edition, 1976 at 20 (hereinafter CRCreference). The term, “specific gravity” as used herein, has itsordinary and customary meaning, that is, the ratio of the density of asubstance to the density of water at 4° C., and the density of water atthis temperature is 1 g/cm³. The specific gravity may be measuredaccording to ASTM test specification ASTM D-792-98. In addition, thecores of this invention typically have a COR of about 0.75 or greater;and preferably about 0.80 or greater. The compression of the overallcore (that is, center and one or more outer core layers) preferably isabout 20 to about 110 and more preferably in the range of about 30 toabout 90. The center (innermost core layer) can have significantly lowercompression and may be less than 10 and preferably less than 20 and morepreferably less than 30.

In one embodiment, a four-piece ball having a multi-layered core ismade. The golf ball comprises: i) an inner core comprising a metalmaterial, the inner core having a diameter in the range of about 0.100to about 1.100 inches, and a specific gravity (SG_(inner)), and an outersurface hardness (H_(center surface)) and a center hardness(H_(center)), the H_(center surface) being greater than the H_(center)to provide a positive hardness gradient. The ball further comprises: ii)an outer core layer comprising a thermoset or thermoplastic material,the outer core layer being disposed about the inner core and having athickness in the range of about 0.200 to about 1.200 inches, a specificgravity (SG_(outer)), and an outer surface hardness(H_(outer surface of OC))and a midpoint hardness (H_(midpoint of OC))the H_(outer surface of OC) being greater than the H_(midpoint of OC) toprovide a positive hardness gradient.

The golf ball also comprises iii) an inner cover having a specificgravity (SG_(inner cover)) and iv) an outer cover having a specificgravity (SG_(outer cover)). The golf balls have one or more thefollowing specific gravity relationship between the layers in the ball:

a) the specific gravity of the inner core (SG_(inner core)) and specificgravity of the inner cover layer (SG_(inner cover)) are substantiallyequal (that is, the difference between the specific gravity values is nogreater than 0.3);

b) the specific gravity of the inner cover layer (SG_(inner cover)) andspecific gravity of the outer cover layer (SG_(outer cover)) aresubstantially equal (that is, the difference between the specificgravity values is no greater than 0.3);

c) the specific gravity of the inner core (SG_(inner core)) and specificgravity of the outer core layer (SG_(outer core layer)) aresubstantially equal (that is, the difference between the specificgravity values is no greater than 0.3); and d) the sum of the specificgravity values of the inner core and inner cover layer[(SG_(inner core))+(SG_(inner cover))] is greater than the sum of thespecific gravity values of the outer core and outer cover layers[(SG_(outer core))+(SG_(outer cover))].

In another version, the inner core may have a positive hardnessgradient; and the outer core layer may have a zero or negative hardnessgradient. In a third version, the inner core may have a zero or negativehardness gradient; and the outer core layer may have a positive hardnessgradient. Still yet, in another version, both the inner core and outercore layers have zero or negative hardness gradients. Such hardnessgradients are discussed further below.

Curing of Rubber Composition

The rubber compositions of this invention may be cured usingconventional curing processes. Suitable curing processes include, forexample, peroxide-curing, sulfur-curing, high-energy radiation, andcombinations thereof. Preferably, the rubber composition contains afree-radical initiator selected from organic peroxides, high energyradiation sources capable of generating free-radicals, and combinationsthereof. In one preferred version, the rubber composition isperoxide-cured. Suitable organic peroxides include, but are not limitedto, dicumyl peroxide; n-butyl-4,4-di(t-butylperoxy) valerate;1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane;2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide;di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoylperoxide; t-butyl hydroperoxide; and combinations thereof. In aparticular embodiment, the free radical initiator is dicumyl peroxide,including, but not limited to Perkadox® BC, commercially available fromAkzo Nobel. Peroxide free-radical initiators are generally present inthe rubber composition in an amount of at least 0.05 parts by weight per100 parts of the total rubber, or an amount within the range having alower limit of 0.05 parts or 0.1 parts or 1 part or 1.25 parts or 1.5parts or 2.5 parts or 5 parts by weight per 100 parts of the totalrubbers, and an upper limit of 2.5 parts or 3 parts or 5 parts or 6parts or 10 parts or 15 parts by weight per 100 parts of the totalrubber. Concentrations are in parts per hundred (phr) unless otherwiseindicated. As used herein, the term, “parts per hundred,” also known as“phr” or “pph” is defined as the number of parts by weight of aparticular component present in a mixture, relative to 100 parts byweight of the polymer component. Mathematically, this can be expressedas the weight of an ingredient divided by the total weight of thepolymer, multiplied by a factor of 100.

The rubber compositions may further include a reactive cross-linkingco-agent. Suitable co-agents include, but are not limited to, metalsalts of unsaturated carboxylic acids having from 3 to 8 carbon atoms;unsaturated vinyl compounds and polyfunctional monomers (e.g.,trimethylolpropane trimethacrylate); phenylene bismaleimide; andcombinations thereof. Particular examples of suitable metal saltsinclude, but are not limited to, one or more metal salts of acrylates,diacrylates, methacrylates, and dimethacrylates, wherein the metal isselected from magnesium, calcium, zinc, aluminum, lithium, and nickel.In a particular embodiment, the co-agent is selected from zinc salts ofacrylates, diacrylates, methacrylates, and dimethacrylates. In anotherparticular embodiment, the agent is zinc diacrylate (ZDA). When theco-agent is zinc diacrylate and/or zinc dimethacrylate, the co-agent istypically included in the rubber composition in an amount within therange having a lower limit of 1 or 5 or 10 or 15 or 19 or 20 parts byweight per 100 parts of the total rubber, and an upper limit of 24 or 25or 30 or 35 or 40 or 45 or 50 or 60 parts by weight per 100 parts of thebase rubber.

Radical scavengers such as a halogenated organosulfur, organicdisulfide, or inorganic disulfide compounds may be added to the rubbercomposition. These compounds also may function as “soft and fastagents.” As used herein, “soft and fast agent” means any compound or ablend thereof that is capable of making a core: 1) softer (having alower compression) at a constant “coefficient of restitution” (COR);and/or 2) faster (having a higher COR at equal compression), whencompared to a core equivalently prepared without a soft and fast agent.Preferred halogenated organosulfur compounds include, but are notlimited to, pentachlorothiophenol (PCTP) and salts of PCTP such as zincpentachlorothiophenol (ZnPCTP). Using PCTP and ZnPCTP in golf ball innercores helps produce softer and faster inner cores. The PCTP and ZnPCTPcompounds help increase the resiliency and the coefficient ofrestitution of the core. In a particular embodiment, the soft and fastagent is selected from ZnPCTP, PCTP, ditolyl disulfide, diphenyldisulfide, dixylyl disulfide, 2-nitroresorcinol, and combinationsthereof.

As discussed above, the compositions of this invention are formulated tohave specific gravity levels so that they can be used to form certaincore components of the golf ball. In addition to the metal fillersdiscussed above, the rubber compositions may contain other additives.Examples of useful fillers include but are not limited to, carbonaceousmaterials such as graphite and carbon black. graphite fibers,precipitated hydrated silica, clay, talc, glass fibers, aramid fibers,mica, calcium metasilicate, barium sulfate, zinc sulfide, silicates,diatomaceous earth, calcium carbonate, magnesium carbonate, rubberregrind (which is recycled uncured rubber material which is mixed andground), cotton flock, natural bitumen, cellulose flock, and leatherfiber. Micro balloon fillers such as glass and ceramic, and fly ashfillers can also be used.

In a particular aspect of this embodiment, the rubber compositionincludes filler(s) selected from carbon black, nanoclays (e.g.,Cloisite® and Nanofil® nanoclays, commercially available from SouthernClay Products, Inc., and Nanomax® and Nanomer® nanoclays, commerciallyavailable from Nanocor, Inc.), talc (e.g., Luzenac HAR® high aspectratio talcs, commercially available from Luzenac America, Inc.), glass(e.g., glass flake, milled glass, and microglass), mica and mica-basedpigments (e.g., Iriodin® pearl luster pigments, commercially availablefrom The Merck Group), and combinations thereof.

In addition, the rubber compositions may include antioxidants to preventthe breakdown of the elastomers. Also, processing aids such as highmolecular weight organic acids and salts thereof may be added to thecomposition. Suitable organic acids are aliphatic organic acids,aromatic organic acids, saturated mono-functional organic acids,unsaturated monofunctional organic acids, multi-unsaturatedmono-functional organic acids, and dimerized derivatives thereof.Particular examples of suitable organic acids include, but are notlimited to, caproic acid, caprylic acid, capric acid, lauric acid,stearic acid, behenic acid, erucic acid, oleic acid, linoleic acid,myristic acid, benzoic acid, palmitic acid, phenylacetic acid,naphthalenoic acid, and dimerized derivatives thereof. The organic acidsare aliphatic, mono-functional (saturated, unsaturated, ormulti-unsaturated) organic acids. Salts of these organic acids may alsobe employed. The salts of organic acids include the salts of barium,lithium, sodium, zinc, bismuth, chromium, cobalt, copper, potassium,strontium, titanium, tungsten, magnesium, cesium, iron, nickel, silver,aluminum, tin, or calcium, salts of fatty acids, particularly stearic,behenic, erucic, oleic, linoelic or dimerized derivatives thereof. It ispreferred that the organic acids and salts of the present invention berelatively non-migratory (they do not bloom to the surface of thepolymer under ambient temperatures) and non-volatile (they do notvolatilize at temperatures required for melt-blending.)

Other ingredients such as accelerators (for example, tetramethylthiuram), processing aids, dyes and pigments, wetting agents,surfactants, plasticizers, coloring agents, fluorescent agents, chemicalblowing and foaming agents, defoaming agents, stabilizers, softeningagents, impact modifiers, antioxidants, antiozonants, as well as otheradditives known in the art may be added to the rubber composition.

Core Structure

The hardness of the core sub-assembly (inner core and outer core layer)is an important property. In general, cores with relatively highhardness values have higher compression and tend to have good durabilityand resiliency. However, some high compression balls are stiff and thismay have a detrimental effect on shot control and placement. Thus, theoptimum balance of hardness in the core sub-assembly needs to beattained.

In one preferred golf ball, the inner core (center) has a “positive”hardness gradient (that is, the outer surface of the inner core isharder than its geometric center); and the outer core layer has a“positive” hardness gradient (that is, the outer surface of the outercore layer is harder than the inner surface of the outer core layer.) Insuch cases where both the inner core and outer core layer each has a“positive” hardness gradient, the outer surface hardness of the outercore layer is preferably greater than the hardness of the geometriccenter of the inner core. In one preferred version, the positivehardness gradient of the inner core is in the range of about 2 to about40 Shore C units and even more preferably about 10 to about 25 Shore Cunits; while the positive hardness gradient of the outer core is in therange of about 2 to about 20 Shore C and even more preferably about 3 toabout 10 Shore C.

In an alternative version, the inner core may have a positive hardnessgradient; and the outer core layer may have a “zero” hardness gradient(that is, the hardness values of the outer surface of the outer corelayer and the inner surface of the outer core layer are substantiallythe same) or a “negative” hardness gradient (that is, the outer surfaceof the outer core layer is softer than the inner surface of the outercore layer.) For example, in one version, the inner core has a positivehardness gradient; and the outer core layer has a negative hardnessgradient in the range of about 2 to about 25 Shore C. In a secondalternative version, the inner core may have a zero or negative hardnessgradient; and the outer core layer may have a positive hardnessgradient. Still yet, in another embodiment, both the inner core andouter core layers have zero or negative hardness gradients.

In general, hardness gradients are further described in Bulpett et al.,U.S. Pat. Nos. 7,537,529 and 7,410,429, the disclosures of which arehereby incorporated by reference. Methods for measuring the hardness ofthe inner core and outer core layers along with other layers in the golfball and determining the hardness gradients of the various layers aredescribed in further detail below. The core layers have positive,negative, or zero hardness gradients defined by hardness measurementsmade at the outer surface of the inner core (or outer surface of theouter core layer) and radially inward towards the center of the innercore (or inner surface of the outer core layer). These measurements aremade typically at 2-mm increments as described in the test methodsbelow. In general, the hardness gradient is determined by subtractingthe hardness value at the innermost portion of the component beingmeasured (for example, the center of the inner core or inner surface ofthe outer core layer) from the hardness value at the outer surface ofthe component being measured (for example, the outer surface of theinner core or outer surface of the outer core layer).

Positive Hardness Gradient. For example, if the hardness value of theouter surface of the inner core is greater than the hardness value ofthe inner core's geometric center (that is, the inner core has a surfaceharder than its geometric center), the hardness gradient will be deemed“positive” (a larger number minus a smaller number equals a positivenumber.) For example, if the outer surface of the inner core has ahardness of 67 Shore C and the geometric center of the inner core has ahardness of 60 Shore C, then the inner core has a positive hardnessgradient of 7. Likewise, if the outer surface of the outer core layerhas a greater hardness value than the inner surface of the outer corelayer, the given outer core layer will be considered to have a positivehardness gradient.

Negative Hardness Gradient. On the other hand, if the hardness value ofthe outer surface of the inner core is less than the hardness value ofthe inner core's geometric center (that is, the inner core has a surfacesofter than its geometric center), the hardness gradient will be deemed“negative.” For example, if the outer surface of the inner core has ahardness of 68 Shore C and the geometric center of the inner core has ahardness of 70 Shore C, then the inner core has a negative hardnessgradient of 2. Likewise, if the outer surface of the outer core layerhas a lesser hardness value than the inner surface of the outer corelayer, the given outer core layer will be considered to have a negativehardness gradient.

Zero Hardness Gradient. In another example, if the hardness value of theouter surface of the inner core is substantially the same as thehardness value of the inner core's geometric center (that is, thesurface of the inner core has about the same hardness as the geometriccenter), the hardness gradient will be deemed “zero.” For example, ifthe outer surface of the inner core and the geometric center of theinner core each has a hardness of 65 Shore C, then the inner core has azero hardness gradient. Likewise, if the outer surface of the outer corelayer has a hardness value approximately the same as the inner surfaceof the outer core layer, the outer core layer will be considered to havea zero hardness gradient.

More particularly, the term, “positive hardness gradient” as used hereinmeans a hardness gradient of positive 3 Shore C or greater, preferably 7Shore C or greater, more preferably 10 Shore C, and even more preferably20 Shore C or greater. The term, “zero hardness gradient” as used hereinmeans a hardness gradient of less than 3 Shore C, preferably less than 1Shore C and may have a value of zero or negative 1 to negative 10 ShoreC. The term, “negative hardness gradient” as used herein means ahardness value of less than zero, for example, negative 3, negative 5,negative 7, negative 10, negative 15, or negative 20 or negative 25. Theterms, “zero hardness gradient” and “negative hardness gradient” may beused herein interchangeably to refer to hardness gradients of negative 1to negative 10.

The inner core preferably has a geometric center hardness(H_(inner core center)) of about 5 Shore D or greater. For example, the(H_(inner core center)) may be in the range of about 5 to about 88 ShoreD and more particularly within a range having a lower limit of about 5or 10 or 15 or 18 or 20 or 26 or 30 or 34 or 36 or 38 or 42 or 48 or 50or 52 Shore D and an upper limit of about 54 or 56 or 58 or 60 or 62 or64 or 68 or 70 or 74 or 76 or 80 or 82 or 84 or 88 Shore D. In anotherexample, the center hardness of the inner core (H_(inner core center)),as measured in Shore C units, is preferably about 10 Shore C or greater;for example, the H_(inner core center) may have a lower limit of about10 or 14 or 16 or 20 or 23 or 24 or 28 or 31 or 34 or 37 or 40 or 44Shore C and an upper limit of about 46 or 48 or 50 or 51 or 53 or 55 or58 or 61 or 62 or 65 or 68 or 71 or 74 or 76 or 78 or 79 or 80 or 84 or90 Shore C. Concerning the outer surface hardness of the inner core(H_(inner core surface)), this hardness is preferably about 12 Shore Dor greater; for example, the H_(inner core surface) may fall within arange having a lower limit of about 12 or 15 or 18 or 20 or 22 or 26 or30 or 34 or 36 or 38 or 42 or 48 or 50 or 52 Shore D and an upper limitof about 54 or 56 or 58 or 60 or 62 or 70 or 72 or 75 or 78 or 80 or 82or 84 or 86 or 90 Shore D. In one version, the outer surface hardness ofthe inner core (H_(inner core surface)), as measured in Shore C units,has a lower limit of about 13 or 15 or 18 or 20 or 22 or 24 or 27 or 28or 30 or 32 or 34 or 38 or 44 or 47 or 48 Shore C and an upper limit ofabout 50 or 54 or 56 or 61 or 65 or 66 or 68 or 70 or 73 or 76 or 78 or80 or 84 or 86 or 88 or 90 or 92 Shore C. In another version, thegeometric center hardness (H_(inner core center)) is in the range ofabout 10 Shore C to about 50 Shore C; and the outer surface hardness ofthe inner core (H_(inner core surface)) is in the range of about 5 ShoreC to about 50 Shore C.

On the other hand, the outer core layer preferably has an outer surfacehardness (H_(outer surface of OC)) of about 40 Shore D or greater, andmore preferably within a range having a lower limit of about 40 or 42 or44 or 46 or 48 or 50 or 52 and an upper limit of about 54 or 56 or 58 or60 or 62 or 64 or 70 or 74 or 78 or 80 or 82 or 85 or 87 or 88 or 90Shore D. The outer surface hardness of the outer core layer(H_(outer surface of OC)), as measured in Shore C units, preferably hasa lower limit of about 40 or 42 or 45 or 48 or 50 or 54 or 58 or 60 or63 or 65 or 67 or 70 or 72 or 73 or 76 Shore C, and an upper limit ofabout 78 or 80 or 84 or 87 or 88 or 89 or 90 or 92 or 95 Shore C. And,the inner surface of the outer core layer (H_(inner surface of OC)) ormidpoint hardness of the outer core layer (H_(midpoint of OC)),preferably has a hardness of about 30 Shore D or greater, and morepreferably within a range having a lower limit of about 30 or 35 or 40or 42 or 44 or 46 or 48 or 50 or 52 and an upper limit of about 54 or 56or 58 or 60 or 62 or 64 or 70 or 74 or 78 or 80 or 82 or 85 or 87 or 88or 90 Shore D. The inner surface hardness (H_(inner surface of OC)) ormidpoint hardness (H_(midpoint of OC)) of the outer core layer, asmeasured in Shore C units, preferably has a lower limit of about 40 or42 or 44 or 45 or 47 or 50 or 52 or 54 or 55 or 58 or 60 or 63 or 65 or67 or 70 or 73 or 75 Shore C, and an upper limit of about 78 or 80 or 85or 88 or 89 or 90 or 92 or 95 Shore C.

The midpoint of a core layer is taken at a point equidistant from theinner surface and outer surface of the layer to be measured, mosttypically an outer core layer. Once one or more core layers surround alayer of interest, the exact midpoint may be difficult to determine,therefore, for the purposes of the present invention, the measurement of“midpoint” hardness of a layer is taken within plus or minus 1 mm of themeasured midpoint of the layer.

In one embodiment, the outer surface hardness of the outer core layer(H_(outer surface of OC)), is inner core surface) midpoint less than theouter surface hardness (H_(inner core surface)) or midpoint hardness(H_(midpoint of OC)), of the inner core by at least 3 Shore C units andmore preferably by at least 5 Shore C.

In a second embodiment, the outer surface hardness of the outer corelayer (H_(outer surface of OC)), is greater than the outer surfacehardness (H_(inner core surface)) or midpoint hardness(H_(midpoint of OC)), of the inner core by at least 3 Shore C units andmore preferably by at least 5 Shore C.

As discussed above, the inner core is preferably formed from a thermosetcomposition such as polybutadiene rubber and the outer core ispreferably formed from a thermoplastic composition such as an ethyleneacid copolymer composition.

The core structure also has a hardness gradient across the entire coreassembly. In one embodiment, the (H_(inner core center)) is in the rangeof about 10 Shore C to about 60 Shore C, preferably about 13 Shore C toabout 55 Shore C; and the (H_(outer surface of OC)) is in the range ofabout 65 to about 96 Shore C, preferably about 68 Shore C to about 94Shore C or about 75 Shore C to about 93 Shore C, to provide a positivehardness gradient across the core assembly. The gradient across the coreassembly will vary based on several factors including, but not limitedto, the dimensions of the inner core, intermediate core, and outer corelayers.

The inner core preferably has a diameter in the range of about 0.100 toabout 1.100 inches. For example, the inner core may have a diameterwithin a range of about 0.100 to about 0.500 inches. In another example,the inner core may have a diameter within a range of about 0.300 toabout 0.800 inches. More particularly, the inner core may have adiameter size with a lower limit of about 0.10 or 0.12 or 0.15 or 0.25or 0.30 or 0.35 or 0.45 or 0.55 inches and an upper limit of about 0.60or 0.65 or 0.70 or 0.80 or 0.90 or 1.00 or 1.10 inches. As far as theouter core layer is concerned, it preferably has a thickness in therange of about 0.100 to about 0.750 inches. For example, the lower limitof thickness may be about 0.050 or 0.100 or 0.150 or 0.200 or 0.250 or0.300 or 0.340 or 0.400 and the upper limit may be about 0.500 or 0.550or 0.600 or 0.650 or 0.700 or 0.750 inches.

The USGA has established a maximum weight of 45.93 g (1.62 ounces) forgolf balls. For play outside of USGA rules, the golf balls can beheavier. In one preferred embodiment, the weight of the multi-layeredcore is in the range of about 28 to about 38 grams. Also, golf ballsmade in accordance with this invention can be of any size, although theUSGA requires that golf balls used in competition have a diameter of atleast 1.68 inches. For play outside of United States Golf Association(USGA) rules, the golf balls can be of a smaller size. Normally, golfballs are manufactured in accordance with USGA requirements and have adiameter in the range of about 1.68 to about 1.80 inches. As discussedfurther below, the golf ball contains a cover which may be multi-layeredand in addition may contain intermediate layers, and the thicknesslevels of these layers also must be considered. Thus, in general, thedual-layer core structure normally has an overall diameter within arange having a lower limit of about 1.00 or 1.20 or 1.30 or 1.40 inchesand an upper limit of about 1.58 or 1.60 or 1.62 or 1.66 inches, andmore preferably in the range of about 1.3 to 1.65 inches. In oneembodiment, the diameter of the core sub-assembly is in the range ofabout 1.45 to about 1.62 inches.

Cover Structure

The golf ball cores of this invention may be enclosed with one or morecover layers. For example, golf ball having inner and outer cover layersmay be made. In addition, as discussed above, an intermediate or casinglayer may be disposed between the core and cover layers. The coverlayers preferably have good impact durability and wear-resistance. Theethylene acid copolymer compositions of this invention may be used toform at least one of the intermediate and/or cover layers.

In one particularly preferred version, the golf ball includes amulti-layered cover comprising inner and outer cover layers. The innercover layer is preferably formed from a composition comprising anionomer or a blend of two or more ionomers that helps impart hardness tothe ball. In a particular embodiment, the inner cover layer is formedfrom a composition comprising a high acid ionomer. A particularlysuitable high acid ionomer is Surlyn 8150® (DuPont). Surlyn 8150® is acopolymer of ethylene and methacrylic acid, having an acid content of 19wt %, which is 45% neutralized with sodium. In another particularembodiment, the inner cover layer is formed from a compositioncomprising a high acid ionomer and a maleic anhydride-graftednon-ionomeric polymer. A particularly suitable maleic anhydride-graftedpolymer is Fusabond 525D® (DuPont). Fusabond 525D® is a maleicanhydride-grafted, metallocene-catalyzed ethylene-butene copolymerhaving about 0.9 wt % maleic anhydride grafted onto the copolymer. Aparticularly preferred blend of high acid ionomer and maleicanhydride-grafted polymer is an 84 wt %/16 wt % blend of Surlyn 8150®and Fusabond 525D®. Blends of high acid ionomers with maleicanhydride-grafted polymers are further disclosed, for example, in U.S.Pat. Nos. 6,992,135 and 6,677,401, the entire disclosures of which arehereby incorporated herein by reference.

The inner cover layer also may be formed from a composition comprising a50/45/5 blend of Surlyn® 8940/Surlyn® 9650/Nucrel® 960, and, in aparticularly preferred embodiment, the composition has a materialhardness of from 80 to 85 Shore C. In yet another version, the innercover layer is formed from a composition comprising a 50/25/25 blend ofSurlyn® 8940/Surlyn® 9650/Surlyn® 9910, preferably having a materialhardness of about 90 Shore C. The inner cover layer also may be formedfrom a composition comprising a 50/50 blend of Surlyn® 8940/Surlyn®9650, preferably having a material hardness of about 86 Shore C. Acomposition comprising a 50/50 blend of Surlyn® 8940 and Surlyn® 7940also may be used. Surlyn® 8940 is an E/MAA copolymer in which the MAAacid groups have been partially neutralized with sodium ions. Surlyn®9650 and Surlyn® 9910 are two different grades of E/MAA copolymer inwhich the MAA acid groups have been partially neutralized with zincions. Nucrel® 960 is an E/MAA copolymer resin nominally made with 15 wt% methacrylic acid.

A wide variety of materials may be used for forming the outer coverincluding, for example, polyurethanes; polyureas; copolymers, blends andhybrids of polyurethane and polyurea; olefin-based copolymer ionomerresins (for example, Surlyn® ionomer resins and DuPont HPF® 1000 andHPF® 2000, commercially available from DuPont; lotek® ionomers,commercially available from ExxonMobil Chemical Company; Amplify® IOionomers of ethylene acrylic acid copolymers, commercially availablefrom The Dow Chemical Company; and Clarix® ionomer resins, commerciallyavailable from A. Schulman Inc.); polyethylene, including, for example,low density polyethylene, linear low density polyethylene, and highdensity polyethylene; polypropylene; rubber-toughened olefin polymers;acid copolymers, for example, poly(meth)acrylic acid, which do notbecome part of an ionomeric copolymer; plastomers; flexomers;styrene/butadiene/styrene block copolymers;styrene/ethylene-butylene/styrene block copolymers; dynamicallyvulcanized elastomers; copolymers of ethylene and vinyl acetates;copolymers of ethylene and methyl acrylates; polyvinyl chloride resins;polyamides, poly(amide-ester) elastomers, and graft copolymers ofionomer and polyamide including, for example, Pebax® thermoplasticpolyether block amides, commercially available from Arkema Inc;cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromDuPont or RiteFlex®, commercially available from Ticona EngineeringPolymers; polyurethane-based thermoplastic elastomers, such asElastollan®, commercially available from BASF; synthetic or naturalvulcanized rubber; and combinations thereof. Castable polyurethanes,polyureas, and hybrids of polyurethanes-polyureas are particularlydesirable because these materials can be used to make a golf ball havinghigh resiliency and a soft feel. By the term, “hybrids of polyurethaneand polyurea,” it is meant to include copolymers and blends thereof.

Polyurethanes, polyureas, and blends, copolymers, and hybrids ofpolyurethane/polyurea are also particularly suitable for forming coverlayers. When used as cover layer materials, polyurethanes and polyureascan be thermoset or thermoplastic. Thermoset materials can be formedinto golf ball layers by conventional casting or reaction injectionmolding techniques. Thermoplastic materials can be formed into golf balllayers by conventional compression or injection molding techniques.

The compositions used to make any cover layer (for example, inner,intermediate, or outer cover layer) may contain a wide variety offillers and additives to impart specific properties to the ball. Forexample, relatively heavy-weight and light-weight metal fillers such as,particulate; powders; flakes; and fibers of copper, steel, brass,tungsten, titanium, aluminum, magnesium, molybdenum, cobalt, nickel,iron, lead, tin, zinc, barium, bismuth, bronze, silver, gold, andplatinum, and alloys and combinations thereof may be used to adjust thespecific gravity of the ball. Other additives and fillers include, butare not limited to, optical brighteners, coloring agents, fluorescentagents, whitening agents, UV absorbers, light stabilizers, surfactants,processing aids, antioxidants, stabilizers, softening agents, fragrancecomponents, plasticizers, impact modifiers, titanium dioxide, clay,mica, talc, glass flakes, milled glass, and mixtures thereof.

The inner cover layer preferably has a material hardness within a rangehaving a lower limit of 70 or 75 or 80 or 82 Shore C and an upper limitof 85 or 86 or 90 or 92 Shore C. The thickness of the intermediate layeris preferably within a range having a lower limit of 0.010 or 0.015 or0.020 or 0.030 inches and an upper limit of 0.035 or 0.045 or 0.080 or0.120 inches. The outer cover layer preferably has a material hardnessof 85 Shore C or less. The thickness of the outer cover layer ispreferably within a range having a lower limit of 0.010 or 0.015 or0.025 inches and an upper limit of 0.035 or 0.040 or 0.055 or 0.080inches. Methods for measuring hardness of the layers in the golf ballare described in further detail below.

A single cover or, preferably, an inner cover layer is formed around theouter core layer. When an inner cover layer is present, an outer coverlayer is formed over the inner cover layer. Most preferably, the innercover is formed from an ionomeric material and the outer cover layer isformed from a polyurethane material, and the outer cover layer has ahardness that is less than that of the inner cover layer. Preferably,the inner cover has a hardness of greater than about 60 Shore D and theouter cover layer has a hardness of less than about 60 Shore D. In analternative embodiment, the inner cover layer is comprised of apartially or fully neutralized ionomer, a thermoplastic polyesterelastomer such as Hytrel™, commercially available form DuPont , athermoplastic polyether block amide, such as Pebax™, commerciallyavailable from Arkema,Inc., or a thermoplastic or thermosettingpolyurethane or polyurea, and the outer cover layer is comprised of anionomeric material. In this alternative embodiment, the inner coverlayer has a hardness of less than about 60 Shore D and the outer coverlayer has a hardness of greater than about 55 Shore D and the innercover layer hardness is less than the outer cover layer hardness.

As discussed above, the core structure of this invention may be enclosedwith one or more cover layers. In one embodiment, a multi-layered covercomprising inner and outer cover layers is formed, where the inner coverlayer has a thickness of about 0.01 inches to about 0.06 inches, morepreferably about 0.015 inches to about 0.040 inches, and most preferablyabout 0.02 inches to about 0.035 inches. In this version, the innercover layer is formed from a partially- or fully-neutralized ionomerhaving a Shore D hardness of greater than about 55, more preferablygreater than about 60, and most preferably greater than about 65. Theouter cover layer, in this embodiment, preferably has a thickness ofabout 0.015 inches to about 0.055 inches, more preferably about 0.02inches to about 0.04 inches, and most preferably about 0.025 inches toabout 0.035 inches, with a hardness of about Shore D 80 or less, morepreferably 70 or less, and most preferably about 60 or less. The innercover layer is harder than the outer cover layer in this version. Apreferred outer cover layer is a castable or reaction injection moldedpolyurethane, polyurea or copolymer, blend, or hybrid thereof having aShore D hardness of about 40 to about 50. In another multi-layer cover,dual-core embodiment, the outer cover and inner cover layer materialsand thickness are the same but, the hardness range is reversed, that is,the outer cover layer is harder than the inner cover layer. For thisharder outer cover/softer inner cover embodiment, the ionomer resinsdescribed above would preferably be used as outer cover material.

Manufacturing of Golf Balls

The inner core may be formed by any suitable technique includingcompression and injection molding methods. The outer core layer, whichsurrounds the inner core, is formed by molding compositions over theinner core. Compression or injection molding techniques may be used toform the other layers of the core sub-assembly. Then, the cover layersare applied over the core sub-assembly. Prior to this step, the corestructure may be surface-treated to increase the adhesion between itsouter surface and the next layer that will be applied over the core.Such surface-treatment may include mechanically or chemically-abradingthe outer surface of the core. For example, the core may be subjected tocorona-discharge, plasma-treatment, silane-dipping, or other treatmentmethods known to those in the art.

The cover layers are formed over the core or ball sub-assembly (the corestructure and any intermediate layers disposed about the core) using asuitable technique such as, for example, compression-molding,flip-molding, injection-molding, retractable pin injection-molding,reaction injection-molding (RIM), liquid injection-molding, casting,spraying, powder-coating, vacuum-forming, flow-coating, dipping,spin-coating, and the like. Preferably, each cover layer is separatelyformed over the ball subassembly. For example, an ethylene acidcopolymer ionomer composition may be injection-molded to producehalf-shells. Alternatively, the ionomer composition can be placed into acompression mold and molded under sufficient pressure, temperature, andtime to produce the hemispherical shells. The smooth-surfacedhemispherical shells are then placed around the core sub-assembly in acompression mold. Under sufficient heating and pressure, the shells fusetogether to form an inner cover layer that surrounds the sub-assembly.In another method, the ionomer composition is injection-molded directlyonto the core sub-assembly using retractable pin injection molding. Anouter cover layer comprising a polyurethane or polyurea composition overthe ball sub-assembly may be formed by using a casting process.

After the golf balls have been removed from the mold, they may besubjected to finishing steps such as flash-trimming, surface-treatment,marking, coating, and the like using techniques known in the art. Forexample, in traditional white-colored golf balls, the white-pigmentedcover may be surface-treated using a suitable method such as, forexample, corona, plasma, or ultraviolet (UV) light-treatment. Then,indicia such as trademarks, symbols, logos, letters, and the like may beprinted on the ball's cover using pad-printing, ink-jet printing,dye-sublimation, or other suitable printing methods. Clear surfacecoatings (for example, primer and top-coats), which may contain afluorescent whitening agent, are applied to the cover. The resultinggolf ball has a glossy and durable surface finish.

In another finishing process, the golf balls are painted with one ormore paint coatings. For example, white primer paint may be appliedfirst to the surface of the ball and then a white top-coat of paint maybe applied over the primer. Of course, the golf ball may be painted withother colors, for example, red, blue, orange, and yellow. As notedabove, markings such as trademarks and logos may be applied to thepainted cover of the golf ball. Finally, a clear surface coating may beapplied to the cover to provide a shiny appearance and protect any logosand other markings printed on the ball.

Different ball constructions can be made using the core construction ofthis invention as shown in FIGS. 1-4. Such golf ball constructionsinclude, for example, one-piece, two-piece, three-piece, four-piece, andfive-piece constructions. It should be understood that the golf ballsshown in FIGS. 1-4 are for illustrative purposes only, and they are notmeant to be restrictive. Other golf ball constructions can be made inaccordance with this invention.

Three-Layered Cores

For example, in another embodiment, a core structure having three layersis formed. One or more of the core layers is formed from a highlyneutralized polymer (“HNP”) composition; one or more of the core layersis formed from a thermoset rubber composition; and one or more of thecore layers is formed from the thermoplastic composition containingmetal of this invention. In a particular embodiment, the core comprises:a) an inner core formed from the thermoplastic composition containingmetal of this invention, b) a thermoplastic HNP intermediate layer, andc) a thermoset rubber outer core layer. In another particularembodiment, the core includes an inner layer formed from a HNPcomposition, b) an intermediate layer formed from a thermoplasticcomposition containing metal of this invention, and c) a thermosetrubber outer core layer. In yet another particular embodiment, the corecomprises: a) an inner core layer formed from a HNP composition, b) athermoset rubber intermediate core layer, and c) thermoplasticcomposition containing metal of this invention. In another version, thecore comprises: i) a thermoset rubber inner core, ii) a firstintermediate core layer formed from a HNP composition, iii) a secondintermediate core layer formed from the thermoplastic compositioncontaining metal of this invention, and iv) a thermoset rubber outercore layer. In yet another version, the core comprises: i) a thermosetrubber inner core layer, ii) an intermediate core layer formed from thethermoplastic composition containing metal of this invention, and iii)an outer core layer formed from a HNP composition. In yet anotherparticular embodiment, the core comprises: i) a thermoset rubber innercore layer, ii) an intermediate core layer formed from the thermoplasticcomposition containing metal of this invention, iii) a secondintermediate core layer formed from a HNP composition, and iv) athermoset rubber outer core layer.

As discussed above, golf balls having various constructions may be madein accordance with this invention. Preferably, a three-piece golf ballhaving a dual-core and single-layered cover or a four-piece ball havinga dual-core and dual-layered cover is made. It is also recognized thattwo-layered and five-layered and even six-layered balls. The inner corecan be made from a thermoplastic composition comprising metal materialas discussed above. For example, referring to FIG. 3, one version of agolf ball that can be made in accordance with this invention isgenerally indicated at (24). The ball (24) is a two-piece ballcontaining a core (26) and surrounding cover (28). In FIG. 4, the golfball (30) contains a dual-core (36 ) having an inner core (center) (36a) and outer core layer (36 b). The dual-core (36) is surrounded by amulti-layered cover (38) having an inner cover layer (38 a) and outercover layer (38 b). An intermediate layer (40) is disposed between thecore (36) and cover (38) sub-structures.

Test Methods

Hardness. The center hardness of a core is obtained according to thefollowing procedure. The core is gently pressed into a hemisphericalholder having an internal diameter approximately slightly smaller thanthe diameter of the core, such that the core is held in place in thehemispherical portion of the holder while concurrently leaving thegeometric central plane of the core exposed. The core is secured in theholder by friction, such that it will not move during the cutting andgrinding steps, but the friction is not so excessive that distortion ofthe natural shape of the core would result. The core is secured suchthat the parting line of the core is roughly parallel to the top of theholder. The diameter of the core is measured 90 degrees to thisorientation prior to securing. A measurement is also made from thebottom of the holder to the top of the core to provide a reference pointfor future calculations. A rough cut is made slightly above the exposedgeometric center of the core using a band saw or other appropriatecutting tool, making sure that the core does not move in the holderduring this step. The remainder of the core, still in the holder, issecured to the base plate of a surface grinding machine. The exposed‘rough’ surface is ground to a smooth, flat surface, revealing thegeometric center of the core, which can be verified by measuring theheight from the bottom of the holder to the exposed surface of the core,making sure that exactly half of the original height of the core, asmeasured above, has been removed to within 0.004 inches. Leaving thecore in the holder, the center of the core is found with a center squareand carefully marked and the hardness is measured at the center markaccording to ASTM D-2240. Additional hardness measurements at anydistance from the center of the core can then be made by drawing a lineradially outward from the center mark, and measuring the hardness at anygiven distance along the line, typically in 2 mm increments from thecenter. The hardness at a particular distance from the center should bemeasured along at least two, preferably four, radial arms located 180°apart, or 90° apart, respectively, and then averaged. All hardnessmeasurements performed on a plane passing through the geometric centerare performed while the core is still in the holder and without havingdisturbed its orientation, such that the test surface is constantlyparallel to the bottom of the holder, and thus also parallel to theproperly aligned foot of the durometer.

The outer surface hardness of a golf ball layer is measured on theactual outer surface of the layer and is obtained from the average of anumber of measurements taken from opposing hemispheres, taking care toavoid making measurements on the parting line of the core or on surfacedefects, such as holes or protrusions. Hardness measurements are madepursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plastic byMeans of a Durometer.” Because of the curved surface, care must be takento ensure that the golf ball or golf ball subassembly is centered underthe durometer indenter before a surface hardness reading is obtained. Acalibrated, digital durometer, capable of reading to 0.1 hardness unitsis used for the hardness measurements. The digital durometer must beattached to, and its foot made parallel to, the base of an automaticstand. The weight on the durometer and attack rate conforms to ASTMD-2240.

In certain embodiments, a point or plurality of points measured alongthe “positive” or “negative” gradients may be above or below a line fitthrough the gradient and its outermost and innermost hardness values. Inan alternative preferred embodiment, the hardest point along aparticular steep “positive” or “negative” gradient may be higher thanthe value at the innermost portion of the inner core (the geometriccenter) or outer core layer (the inner surface)—as long as the outermostpoint (i.e., the outer surface of the inner core) is greater than (for“positive”) or lower than (for “negative”) the innermost point (i.e.,the geometric center of the inner core or the inner surface of the outercore layer), such that the “positive” and “negative” gradients remainintact.

As discussed above, the direction of the hardness gradient of a golfball layer is defined by the difference in hardness measurements takenat the outer and inner surfaces of a particular layer. The centerhardness of an inner core and hardness of the outer surface of an innercore in a single-core ball or outer core layer are readily determinedaccording to the test procedures provided above. The outer surface ofthe inner core layer (or other optional intermediate core layers) in adual-core ball are also readily determined according to the proceduresgiven herein for measuring the outer surface hardness of a golf balllayer, if the measurement is made prior to surrounding the layer with anadditional core layer. Once an additional core layer surrounds a layerof interest, the hardness of the inner and outer surfaces of any inneror intermediate layers can be difficult to determine. Therefore, forpurposes of the present invention, when the hardness of the inner orouter surface of a core layer is needed after the inner layer has beensurrounded with another core layer, the test procedure described abovefor measuring a point located 1 mm from an interface is used.

Also, it should be understood that there is a fundamental differencebetween “material hardness” and “hardness as measured directly on a golfball.” For purposes of the present invention, material hardness ismeasured according to ASTM D2240 and generally involves measuring thehardness of a flat “slab” or “button” formed of the material. Surfacehardness as measured directly on a golf ball (or other sphericalsurface) typically results in a different hardness value. The differencein “surface hardness” and “material hardness” values is due to severalfactors including, but not limited to, ball construction (that is, coretype, number of cores and/or cover layers, and the like); ball (orsphere) diameter; and the material composition of adjacent layers. Italso should be understood that the two measurement techniques are notlinearly related and, therefore, one hardness value cannot easily becorrelated to the other. Shore hardness (for example, Shore C or Shore Dhardness) was measured according to the test method ASTM D-2240.

Compression. As disclosed in Jeff Dalton's Compression by Any OtherName, Science and Golf IV, Proceedings of the World Scientific Congressof Golf (Eric Thain ed., Routledge, 2002) (“J. Dalton”), severaldifferent methods can be used to measure compression, including Atticompression, Riehle compression, load/deflection measurements at avariety of fixed loads and offsets, and effective modulus. For purposesof the present invention, “compression” refers to Atti compression andis measured according to a known procedure, using an Atti compressiontest device, wherein a piston is used to compress a ball against aspring. The travel of the piston is fixed and the deflection of thespring is measured. The measurement of the deflection of the spring doesnot begin with its contact with the ball; rather, there is an offset ofapproximately the first 1.25 mm (0.05 inches) of the spring'sdeflection. Very low stiffness cores will not cause the spring todeflect by more than 1.25 mm and therefore have a zero compressionmeasurement. The Atti compression tester is designed to measure objectshaving a diameter of 42.7 mm (1.68 inches); thus, smaller objects, suchas golf ball cores, must be shimmed to a total height of 42.7 mm toobtain an accurate reading. Conversion from Atti compression to Riehle(cores), Riehle (balls), 100 kg deflection, 130-10 kg deflection oreffective modulus can be carried out according to the formulas given inJ. Dalton. Compression may be measured as described in McNamara et al.,U.S. Pat. No. 7,777,871, the disclosure of which is hereby incorporatedby reference.

Coefficient of Restitution (“COR”). The COR is determined according to aknown procedure, wherein a golf ball or golf ball subassembly (forexample, a golf ball core) is fired from an air cannon at two givenvelocities and a velocity of 125 ft/s is used for the calculations.Ballistic light screens are located between the air cannon and steelplate at a fixed distance to measure ball velocity. As the ball travelstoward the steel plate, it activates each light screen and the ball'stime period at each light screen is measured. This provides an incomingtransit time period which is inversely proportional to the ball'sincoming velocity. The ball makes impact with the steel plate andrebounds so it passes again through the light screens. As the reboundingball activates each light screen, the ball's time period at each screenis measured. This provides an outgoing transit time period which isinversely proportional to the ball's outgoing velocity. The COR is thencalculated as the ratio of the ball's outgoing transit time period tothe ball's incoming transit time period(COR=V_(out)/V_(in)=T_(in)/T_(out)).

When numerical lower limits and numerical upper limits are set forthherein, it is contemplated that any combination of these values may beused. Other than in the operating examples, or unless otherwiseexpressly specified, all of the numerical ranges, amounts, values andpercentages such as those for amounts of materials and others in thespecification may be read as if prefaced by the word “about” even thoughthe term “about” may not expressly appear with the value, amount orrange. Accordingly, unless indicated to the contrary, the numericalparameters set forth in the specification and attached claims areapproximations that may vary depending upon the desired propertiessought to be obtained by the present invention.

The present invention is illustrated by the following Examples, butthese Examples should not be construed as limiting the scope of theinvention.

EXAMPLE A

In this Example A, four-piece golf ball samples having a polybutadienerubber inner core; HNP thermoplastic outer core layer; ethylene acidcopolymer ionomer inner cover; and polyurethane (thin, dense layer)outer cover are made. The diameter of the inner core is about 0.25inches. The diameter of the core sub-assembly (inner core and outer corelayer) is in the range of about 1.53 to about 1.58 inches; the diameterof the three-layered intermediate ball (inner core, outer core layer,inner cover) is about 1.62 inches; and the diameter of the finalfour-piece ball (inner core, outer core layer, inner cover, and outercover) is about 1.68 inches.

TABLE I Dimensions and Specific Gravity Relationships of Layers In4-Piece Balls Outer Cover Inner Core Outer Core Inner Cover DimensionsDimensions and Dimensions and Dimensions and and Specific SampleSpecific Gravity Specific Gravity Specific Gravity Gravity A-1 Diameterof Inner Diameter of Inner Diameter of Inner Diameter of Core = 0.25″Core + Outer Core = Core + Outer Core + Inner Core + Specific Gravity of1.53″ Inner Cover = Outer Core + Inner Core = 1.91 Specific Gravity of1.62″ Inner Cover + Outer Core = 0.95 Specific Gravity of Outer Cover =Inner Cover = 1.91 1.68″ Specific Gravity of Outer Cover = 1.13 A-2Diameter of Inner Diameter of Inner Diameter of Inner Diameter of Core =0.25″ Core + Outer Core = Core + Outer Core + Inner Core + SpecificGravity of 1.55″ Inner Cover = Outer Core + Inner Core = 2.16 SpecificGravity of 1.62″ Inner Cover + Outer Core = 0.95 Specific Gravity ofOuter Cover = Inner Cover = 2.16 1.68″ Specific Gravity of Outer Cover =1.13 A-3 Inner Core Inner Core + Outer Inner Core + Outer Inner Core +Diameter of 0.25″ Core Diameter of Core + Inner Cover Outer Core +Specific Gravity of 1.58″ Diameter of 1.62″ Inner Cover + 2.98 SpecificGravity of Specific Gravity of Outer Cover 0.95 2.98 Diameter of 1.68″Specific Gravity of 1.13

As shown in above Table I, in these Samples, the specific gravity of theinner core layer (SG_(inner core)) and specific gravity of the innercover layer (SG_(inner cover)) are substantially equal.

In this Example B, four-piece golf ball samples having a polybutadienerubber inner core; HNP thermoplastic outer core layer; ethylene acidcopolymer ionomer inner cover; and polyurethane (thin, dense layer)outer cover are made. The diameter of the inner core is about 0.25inches. The diameter of the core sub-assembly (inner core and outer corelayer) is in the range of about 1.53 to about 1.58 inches; the diameterof the three-layered intermediate ball (inner core, outer core layer,inner cover) is about 1.62 inches; and the diameter of the finalfour-piece ball (inner core, outer core layer, inner cover, and outercover) is about 1.68 inches.

TABLE II Dimensions and Specific Gravity Relationships of Layers In4-Piece Balls Outer Cover Inner Core Outer Core Inner Cover DimensionsDimensions and Dimensions and Dimensions and and Specific SampleSpecific Gravity Specific Gravity Specific Gravity Gravity B-1 Diameterof Inner Diameter of Inner Diameter of Inner Diameter of Core = 0.25″Core + Outer Core = Core + Outer Core + Inner Core + Specific Gravity of1.53″ Inner Cover = Outer Core + Inner Core = 2.02 Specific Gravity of1.62″ Inner Cover + Outer Core = 0.95 Specific Gravity of Outer Cover =Inner Cover = 2.02 1.68″ Specific Gravity of Outer Cover = 0.95 B-2Diameter of Inner Diameter of Inner Diameter of Inner Diameter of Core =0.25″ Core + Outer Core = Core + Outer Core = Inner Core + SpecificGravity of 1.55″ 1.62″ Outer Core + Inner Core = 2.30 Specific Gravityof Specific Gravity of Inner Cover + Outer Core = 0.95 Outer Core = 2.30Outer Cover = 1.68″ Specific Gravity of Outer Cover = 0.95 B-3 Diameterof Inner Diameter of Inner Diameter of Inner Diameter of Core = 0.25″Core + Outer Core = Core + Outer Core = Inner Core + Specific Gravity of1.58″ 1.62″ Outer Core + Inner Core = 3.23 Specifc Gravity of SpecificGravity of Inner Cover + Outer Core = 0.95 Outer Core = 3.23 Outer Cover= 1.68″ Specific Gravity of Outer Cover = 0.95

EXAMPLE B

As shown in above Table II, in these Samples, the specific gravity ofthe inner core (SG_(inner core)) and specific gravity of the inner cover(SG_(inner cover)) are substantially equal. Also, in these Samples, thespecific gravity of the outer core (SG_(outer core)) and specificgravity of the outer cover (SG_(outer cover)) are substantially equal.

Also, in these Samples, the sum of the Specific Gravity values of theinner core and inner cover layer [(SG_(inner core))+(SG_(inner cover))]is greater than the sum of the Specific Gravity values of the outer coreand outer cover layers [(SG_(outer core))+(SG_(outer cover))].

All patents, publications, test procedures, and other references citedherein, including priority documents, are fully incorporated byreference to the extent such disclosure is not inconsistent with thisinvention and for all jurisdictions in which such incorporation ispermitted.

It is understood that the compositions and golf ball products describedand illustrated herein represent only some embodiments of the invention.It is appreciated by those skilled in the art that various changes andadditions can be made to compositions and products without departingfrom the spirit and scope of this invention. It is intended that allsuch embodiments be covered by the appended claims.

We claim:
 1. A golf ball having a multi-layered core, comprising: i) aninner core comprising a metal material, the inner core having a diameterin the range of about 0.100 to about 1.100 inches, and a specificgravity (SG_(inner core)), and an outer surface hardness(H_(inner core surface)) and a center hardness (H_(inner core)), theH_(inner core surface) being greater than the H_(inner core) to providea positive hardness gradient; ii) an outer core layer comprising athermoset material, the outer core layer being disposed about the innercore and having a thickness in the range of about 0.200 to about 1.200inches, a specific gravity (SG_(outer core)), and an outer surfacehardness (H_(outer surface of OC)) and a midpoint hardness(H_(midpoint of OC)), the H_(outer surface of OC) being greater than theH_(midpoint of OC) to provide a positive hardness gradient; the innercore and outer core forming a core subassembly, wherein theH_(inner core) is in the range of about 65 to about 90 Shore C and theH_(outer surface of OC) is in the range of about 65 to about 96 Shore Cto provide positive hardness gradient across the core assembly; and iii)an inner cover disposed about the multi-layered core, the inner coverhaving a specific gravity (SG_(inner cover)), the SG_(inner core) andSG_(inner cover) being substantially equal; and iv) an outer coverdisposed about the inner cover.
 2. The golf ball of claim 1, wherein themetal material of the inner core is a metal selected from the groupconsisting of copper, steel, brass, tungsten, titanium, aluminum,magnesium, molybdenum, cobalt, nickel, iron, tin, bronze, silver, gold,and platinum, and alloys and combinations thereof.
 3. The golf ball ofclaim 1, wherein the inner core has a diameter in the range of about0.100 to about 0.500 inches.
 4. The golf ball of claim 1, wherein theinner core has a specific gravity in the range of about 1.40 to about6.75.
 5. The golf ball of claim 1, wherein the outer core layer has athickness in the range of about 0.250 to about 0.750 inches.
 6. The golfball of claim 1, wherein the outer core layer comprises a thermosetrubber material selected from the group consisting of polybutadiene,ethylene-propylene rubber, ethylene-propylene-diene rubber,polyisoprene, styrene-butadiene rubber, polyalkenamers, butyl rubber,halobutyl rubber, polystyrene elastomers, copolymers of isobutylene andp-alkylstyrene, halogenated copolymers of isobutylene andp-alkylstyrene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and mixtures thereof.
 7. Agolf ball having a multi-layered core, comprising: i) an inner corecomprising a metal material, the inner core having a diameter in therange of about 0.100 to about 1.100 inches, and a specific gravity(SG_(inner core)), and an outer surface hardness(H_(inner core surface)) and a center hardness (H_(inner core)), theH_(inner core surface) being greater than the H_(inner core) to providea positive hardness gradient; ii) an outer core layer comprising athermoset material, the outer core layer being disposed about the innercore and having a thickness in the range of about 0.200 to about 1.200inches, a specific gravity (SG_(onter core)), and an outer surfacehardness (H_(outer surface of OC)) and a midpoint hardness(H_(midpoint of OC)), the H_(outer surface of OC) being greater than theH_(midpoint of OC) to provide a positive hardness gradient; the innercore and outer core forming a core subassembly, wherein theH_(inner core) is in the range of about 65 to about 90 Shore C and theH_(outer surface of OC) is in the range of about 65 to about 96 Shore Cto provide positive hardness gradient across the core assembly; and iii)an inner cover disposed about the multi-layered core; and iv) an outercover disposed about the inner cover, the outer cover having a specificgravity (SG_(outer cover)), the SG_(outer core) and SG_(outer cover)being substantially equal.
 8. The golf ball of claim 7, wherein themetal material of the inner core is a metal selected from the groupconsisting of copper, steel, brass, tungsten, titanium, aluminum,magnesium, molybdenum, cobalt, nickel, iron, tin, bronze, silver, gold,and platinum, and alloys and combinations thereof.
 9. The golf ball ofclaim 7, wherein the outer core has a specific gravity in the range ofabout 0.50 to about 6.25 g/cc.
 10. The golf ball of claim 7, wherein theinner cover layer and outer cover layer, each has a surface hardness,and the surface hardness of the inner cover layer is greater than thesurface hardness of the outer cover layer.
 11. The golf ball of claim 7,wherein at least one of the inner and outer cover layers is formed froma composition comprising a polymer selected from the group consisting ofethylene acid copolymer ionomers, polyesters; polyamides,polyamide-ethers, polyamide-esters; polyurethanes, polyureas;fluoropolymers; polystryenes; polypropylenes and polyethylenes;polyvinyl chlorides; polyvinyl acetates; polycarbonates; polyvinylalcohols; polyethers; polyimides; polyetherktones; polyamideimides; andmixtures thereof.